essential knowledge: the chromosomal basis of … · dominant phenotype, unknown genotype: pp or...

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Essential knowledge: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring


Objective: You will be able to construct a representation that connects the process of meiosis to the passage of traits from parent to offspring.

Do Now:

Turn to page 206 in your textbook


Some genetic vocabulary

Character: a heritable feature, such as flower color

Genes code for characters

Trait: a variant of a character, such as purple or

white flowers

Alleles are the alternative traits

Turn to a partner and come up with 3 genes for

human characteristics

Provide 2 alleles for each


Individual Activity

Create a drawing of a pea plant cell undergoing meiosis

The cell contains the 4 chromosomes seen below during

the G1 phase of the cell cycle.

Follow the movements of the genes and alleles carefully.

Include both cells of meiosis II

Y = Yellow color

y = Green color

R = Round shape

r = Wrinkled shape


Work with a partner

Do all of your gametes have a “Y” as opposed to a “y”? Find

where in your drawings this occurred.

Randomly put your finger on one of your gametes

If your egg cell fused with your partners sperm cell, what

color would the pea have? (This is fertilization)

Repeat the process with another pair of gametes

What percent chance is their in forming a zygote that

would have yellow color? Green?

How would the percentages change if “R’s” were used?

Y = Yellow color

y = Green color

R = Round shape

r = Wrinkled shape


Objective: You will be able to construct a representation that connects the process of meiosis to the passage of traits from parent to offspring.

Do Now:

Take out your drawings


Find someone that had different gametes than you

• Figure out exactly where in the drawings the difference began

Randomly put your finger on one of your gametes

If your egg cell fused with your partners sperm cell, what

color AND shape would the pea have? (This is fertilization)

Repeat the process with another pair of gametes

What percent chance is their in forming a zygote that would

be:

• Yellow AND Round

• Yellow and Wrinkled

• Green AND Round

• Green and Wrinkled

Y = Yellow color

y = Green color

R = Round shape

r = Wrinkled shape


Punnett Squares

Rules of probability can be applied to analyze

passage of single gene traits from parent to

offspring

YY x yy

Law of

Segregation

Law of

Independent

Assortment

YyRr x YyRr


Monohybrid Cross (Segregation)

• Refers to the mating of two heterozygous individuals

involving one gene

Yy x Yy

Dihybrid Cross (Independent Assortment)

• Refers to the mating of two heterozygous individuals

involving two genes

YyRr x YyRr


Phenotype

vs.

Genotype

Mate a pea plant that is

heterozygous for pod shape

with a plant that is

homozygous recessive

Mate a pea plant that is axial

for flower position with one

that is terminal.

What do you need to know?


Figure 11.7 Technique

Predictions

Dominant phenotype, unknown genotype:

PP or Pp?

Eggs

Sperm

½ offspring purple and

½ offspring white

Recessive phenotype, known genotype:

pp

If purple-flowered parent is PP

If purple-flowered parent is Pp

Eggs

Sperm

All offspring purple

Results

or

or

p p

P

p

Pp

pp

Pp

pp

p p

P

P

Pp

Pp

Pp

Pp

The

Testcross


Objective: You will be able to apply mathematical routines to

determine patterns of inheritance.

Do Now:

A new way to solve genetic problems

• Turn to page 234 and try question 6(a).

• Work with a partner to complete the following

problems in this order: – 6 (b-d)

– 12

– 11

– 9


• Pedigree charts can be used to determine

Mendelian patterns of inheritance.


Figure 11.14a

WW

or

Ww

ww

ww ww

ww ww

Ww Ww

Ww Ww

Widow’s peak

ww Ww

1st generation (grandparents)

3rd generation (two sisters)

2nd generation (parents, aunts, and uncles)

Affected male

Affected female

Male

Female

Key

Mating

Offspring, in birth order (first-born on left)

(a) Is a widow’s peak a dominant or recessive trait?

No widow’s peak


Figure 11.14b

Affected male

Affected female

Male

Female

Key

Mating

Offspring, in birth order (first-born on left)

1st generation (grandparents)

3rd generation (two sisters)

2nd generation (parents, aunts, and uncles)

Attached earlobe Free earlobe

FF

or

Ff

ff

ff ff

Ff ff

Ff FF or

Ff

Ff Ff

ff Ff

(b) Is an attached earlobe a dominant or recessive trait?


• What would you look for in a pedigree chart to determine if a trait

was dominant and not recessive?

• Does this trace a dominant or recessive trait?


Objective: You will be able to solve problems involving

sex-linked traits.

• Do Now:

– Draw a Punnett square that proves which gender is

responsible for the sex of the child.

– List two examples of sex linked-traits in humans

5


Autosomes versus Sex Chromosomes


Sex-linked genes exhibit unique patterns of

inheritance


Some traits are determined by genes on sex chromosomes

• Some traits are sex limited, and expression depends on the sex

of the individual, such as: • Milk production in female mammals

• Male pattern baldness in males

• Color Blindness

• Hemophilia

• In mammals and flies, the Y chromosome is very small and

carries few genes

• Sex-linked genes reside on sex chromosomes (X in humans)

• In mammals and flies, females are XX and males are XY; as

such, X-linked traits are always expressed in males


Do Now:

Take out your meiosis drawings from a few last week

Objective: You will be able to apply mathematical routines to

determine patterns of inheritance involving gene linkage.


Gene Linkage

• Genes that are adjacent and close to each other on the

same chromosome tend to move as a unit.


Gene Linkage

• A cell in G1

• How is this different from independent

assortment?

Y y

R r


Are these two genes linked?

Mate: YyRr x yyrr

Start by drawing the chromosomes and their

genes for the highlighted individual above

OR

• If they are linked, what should the F1 ratio be?

• If they are not linked what should the F1 ratio be?

Unlinked Linked


Experiment

P Generation

(homozygous)

Wild type (gray body, normal wings)

F1 dihybrid testcross

Wild-type F1 dihybrid

(gray body, normal wings)

b b vg vg

b b vg vg

b b vg vg

b b vg vg

Double mutant (black body, vestigial wings)

Homozygous recessive (black body, vestigial wings)

If the two genes are on the same chromosome

(linked), what is the expected F1 ratio


Figure 12.9b

b b vg vg b b vg vg b b vg vg b b vg vg

Eggs

Sperm

b vg

b vg b vg b vg b vg

Wild-type (gray-normal)

Black- vestigial

Gray- vestigial

Black- normal

Experiment

Testcross

offspring

PREDICTED RATIOS

Genes on different

chromosomes:

Genes on same

chromosome:

Results : 965 944 206 185 : :

: : :

: : : 1 1 1 1

1 1 0 0

?


Gene Linkage

• The probability that they will segregate as a unit is a

function of the distance between them.


Y y

R r

Which would show more crossing over?

R Y y

r

O

R


• The recombination frequency is the percentage of the

offspring that were a result of crossing over

• Which scenario would produce offspring with the highest

recombination frequency?


Do Now:

Compile of list of human disorders that are

linked to genetics

Objective: You will be able to pose questions about ethical,

social or medical issues surrounding human genetic disorders.


Certain human genetic disorders can be attributed to the

inheritance of single gene traits or specific

chromosomal changes, such as nondisjunction.

Examples: – Sickle cell anemia (rec.)

– Tay-Sachs disease(rec.)

– Huntington’s disease (dom.)

– X-linked color blindness(rec.)

– Trisomy 21/Down syndrome

– Klinefelter’s syndrome

Single gene traits

Nondisjunction


Figure 12.13-3 Meiosis I

Nondisjunction

Meiosis II

Non- disjunction

Gametes

Number of chromosomes

Nondisjunction of homo- logous chromosomes in meiosis I

(a) (b) Nondisjunction of sister chromatids in meiosis II

n 1 n 1 n 1 n − 1 n − 1 n − 1 n n


Figure 12.15

Trisomy 22/Down Syndrome


Figure 12.14

(a) Deletion (c) Inversion

A deletion removes a chromosomal segment.

(b) Duplication (d) Translocation

An inversion reverses a segment within a chromosome.

A translocation moves a segment from one chromosome to a nonhomologous chromosome.

A duplication repeats a segment.


Many ethical, social and medical issues surround human

genetic disorders.

Examples

– Reproductive issues

– Civic issues such as:

• Ownership of genetic information

• Privacy

Work with a partner to pose FIVE questions about ethical, social

or medical issues surrounding human genetic disorders.


Do Now:

Objective: You will be able to explain deviations from Mendel’s

model of the inheritance of traits.


Essential knowledge: The inheritance pattern of many

traits cannot be explained by simple Mendelian genetics

• Many traits are the products of multiple genes and/or

physiological processes.

– Examples include:

– Sex-linkage

– Incomplete dominance

– Codominance

– Polygenic inheritance

• Patterns of these traits don’t follow ratios predicted

by Mendel’s laws.

• They can be identified by quantitative analysis where

phenotypic ratios differ from predicted ratios.

How does this deviate from Mendel’s patterns?


Make some predictions of what you would expect if these

example followed the inheritance pattern of Mendel.


? How does this deviate

from Mendel’s patterns?

Predict what would

happen in the F2

generation.


Figure 11.10-3

Eggs

½ ½

½

½

P Generation

F1 Generation

Gametes

F2 Generation

Gametes

Sperm

White CWCW

Pink CRCW

Red CRCR

CWCW

CRCW CRCR

CW CR

CW CR

½ ½ CW CR

CW

CR

CRCW

Incomplete

Dominance


Red Bull

RR White Cow

WW

Make some predictions of what you would expect if these

example followed the inheritance pattern of Mendel.


Red Bull

RR White Cow

WW

Roan Cattle

How does this

deviate from

Mendel’s patterns?

Predict what would

happen in the F2

generation.


Figure 11.11

Carbohydrate

(b) Blood group genotypes and phenotypes

Allele

Red blood cell appearance

Genotype

none B A

IB

Phenotype (blood group)

i IA

IAIB ii IAIA or IAi IBIB or IBi

B A O AB

(a) The three alleles for the ABO blood groups and their carbohydrates


Figure 11.13

Eggs

Sperm

AaBbCc AaBbCc

Phenotypes:

0 Number of dark-skin alleles: 1 2 3 4 5 6

1 64

1 64

6 64

6 64

1 64

15 64

15 64

20 64

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

1 8

Polygenic

Inheritance

How would you

know if a

phenotype was

likely controlled by

many genes?


Some traits result from nonnuclear inheritance

• Chloroplasts and mitochondria are randomly assorted to gametes and

daughter cells; thus, traits determined by chloroplast and mitochondrial

DNA do not follow simple Mendelian rules.

• In animals, mitochondrial DNA is transmitted by the egg and not by the

sperm; as such, mitochondrial-determined traits are maternally inherited.


Figure 4.17

Free ribosomes in the mitochondrial matrix

Mitochondrion

Intermembrane space

Matrix

Cristae

DNA

Outer membrane

Inner membrane

0.1 m


Figure 4.18

Intermembrane space

Ribosomes

Inner and outer membranes

1 m

Stroma

Granum

DNA

Chloroplast

Thylakoid

(a) Diagram and TEM of chloroplast

50 m

(b) Chloroplasts in an algal cell

Chloroplasts (red)


A poker-dealing machine is supposed to deal cards at random, as if from an

infinite deck.

In a test, you counted 1600 cards. What would be your expected values for

each suit?

You observed the following:

Spades 404

Hearts 420

Diamonds 400

Clubs 376

• Are these discrepancies too much to be random? Or are they in the realm

of probability?

• Scientists use chi-square as a statistical method that assesses the goodness

of fit between observed values and those expected.


Category

(Suit)

Observed (o) Expected (e) (o-e)2/e

Spades

Hearts

Diamonds

Clubs

X2 =

∑


Spades (404 -400)2/400 = 0.04

Hearts (420-400)2/400= 1.0

Diamonds (400-400)2/400= 0.0

Clubs (376-400)2/400= 1.44_____

X2 = 2.48

So…are these discrepancies too much to be random? Or are they

in the realm of probability?


Do Now:

Objective: You will be able to use the chi square test to determine if

there are significant differences between expected and observed results.


In the garden pea, yellow cotyledon color is dominant to green,

and inflated pod shape is dominant to the constricted form. In a

dihybrid mating, the progeny appeared in the following numbers:

556 yellow, inflated

193 green, inflated

184 yellow constricted

61 green, constricted

Total offspring is 994

Do these genes assort independently? Support your answer using

Chi-square analysis.


Figure 12.UN03b

Dihybrid x homozygous recessive

mating


The Null Hypothesis

• A null hypothesis(H0) is a hypothesis that says there

is no statistical significance between the two

variables.

• It is usually the hypothesis a researcher or

experimenter will try to disprove or discredit.

• An alternative hypothesis is one that states there is a

statistically significant relationship between two

variables.


• Let's say you feed chocolate to a bunch of chickens,

then look at the sex ratio in their offspring. – If you get more females than males, it would be a tremendously

exciting discovery: female chickens are more valuable than male

chickens in egg-laying breeds

– You might look at 48 offspring of chocolate-fed chickens and see 31

females and only 17 males.

– You need to ask "What's the probability of getting a deviation from the

null expectation

– Only when that probability is low can you reject the null hypothesis.

The goal of statistical hypothesis testing is to estimate the probability of

getting your observed results under the null hypothesis.

essential knowledge: the chromosomal basis of … · dominant phenotype, unknown genotype: pp or...

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