Genetics

Gregor Mendel

• 1840’s• Austrian Monk• Tended garden, became interested in

characteristics of plants• “Father of Genetics”

2 laws of Heredity

• 1-Law of segregation• 2-Law of independent assortment

Mendel and his Peas• Analyzed 7

characteristics (traits) of pea plants….size, color, seed texture, flowers present, height

• Cross-pollinated various traits to view outcome

Fig. 23AaCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

stigmastyle

stamen

carpel

Flower Structure

Ovulesin ovary

antherfilament

Fig. 23AbCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cutting awayanthers

Brushing onpollen fromanother plant

All peas are yellow whenone parent produces yellowseeds and the other parentproduces green seeds.

Cross Pollination vs. Self Pollination

What he noticed…• Tall plants mixed with short plants always produced tall plants• However….the offspring of the above plants sometimes produced

short plants in the 2nd generation

What does this mean?

• If a tall plant mixes with a short plant and the offspring are all tall, tall must be a DOMINANT TRAIT and the tall parents must have been PURE BRED

Punnet Square

• Used to show probability of trait expression when combining 2 parents genes (F1 generation)

• T-tall• t-short

When offspring self pollinated….why were some short?

• The offspring of the self pollinated pea plants produced short plants because they were not TRUE BREEDING (pure bred), they had a recessive short gene hidden. (F2 generation)

• T-tall• t-short

Allele

Gene for a specific trait*Everyone has 2 alleles for a specific trait (1

from mom and 1 from dad)If a pea plant height is Tt, they got one T from

one parent and the t from the other parent

Dominant and Recessive Alleles

• Dominant alleles will be expressed (you will SEE the trait) over the recessive allele

• Recessive alleles will be hidden by the dominant allele but will still be a part of the persons genotype (gene combination for a specific trait)

• The only way a recessive allele will be expressed is in the absence of a dominant allele or when 2 recessive alleles are present.

Vocab for alleles

• Homozygous dominant, pure bred dominant, true breeding dominant-ALL mean that the genotype is 2 dominant genes (TT)

• Homozygous recessive, pure bred recessive, true bred recessive-ALL mean that the genotype is 2 recessive genes (tt)

• Heterozygous-Alleles for a genotype are different, one recessive, one dominant (Tt) *Can also be called HYBRID

Genotype and Phenotype

• Genotype-gene or allele combination for a specific trait

• Phenotype-what characteristic is physically seen from the genotype

• Can be expressed in ratios or percentages

• Ex- Tt is genotype, Tall is the phenotype

Practice Punnets

• Round seeds in pea plants are dominant to wrinkled seeds. Self fertilize a heterozygous pea plant. R-round, r-wrinkled

• Genotype:• Phenotype:

• Purple are dominant flowers in pea plants over white flowers. Cross a homozygous dominant, with a homozygous recessive.

• Purple-P, white-p

• Genotype:• Phenotype:

• Yellow seeds are dominant to green seeds in pea plants. Cross a homozygous recessive with a heterozygous. Y-yellow, y-green

• Genotype:

• Phenotype:

Mendel's Laws

• 1-Law of segregation…..Alleles split into each offspring box

• 2-Law of independent assortment…..alleles sort out randomly in each offspring box completely independent of other genes (by chance)

In humans• Eye color• Ears• Widows peak• Pinky fingers• Interlocking fingers??? (weird)

Fig. 23.6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3

MEIOSIS I

MEIOSIS II

either or

one pair

one pair

S

S

S

W

W

W

s

s

s

w w

w

W Ww w

W W

W W W W

sWSwswSW

w w w w

WW w ww w

s s

s ss

s s s s

s

S S

S

S S S S

SS S

Allele KeyW = Widow’s peakw = Straight hairlineS = Short fingerss = Long fingers

Cell hastwo pairs ofhomologues.

Is it possible to get a white flowered pea plant from 2 purple

flowered plants?

•

Try These!!

• Cross a pure bred tall plant with a heterozygous tall plant. List genotypes and phenotypes

• Cross a heterozygous round seeded plant with a wrinkled seeded plant. List genotypes and phenotypes

Is it possible to do a punnett square using more than one trait?

• Try this one….cross a heterozygous purple plant, homozygous tall plant with a homozygous white plant, heterozygous tall plant. List genotypes and phenotypes

Co-Dominance

Try this one:

• Fur color in cats is co-dominant. Cross a Black male with an Orange female.

• *When you are done….Cross 2 orange cats…

Fig. 23.13

Offspring

oocytes

sper

m

Straight hair

Curly hair

Key

121

Phenotypic Ratio

A person with naturally curlyhair (H1H1)

A person with straight hair(H1H1)

HeterozygousParents (H1 H2)

H1 H2 H1 H2

H1 H1

H1 H2 H2 H2

H1 H2H1

H2

H1 H2

Wavy hair

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(man): © Vol. 88/PhotoDisc; (woman): © Larry Williams/Corbis

♀♂

♀♂

Incomplete Dominance

Try this one:

Hair color in mice is incompletely dominant. Cross a Black mouse with a white mouse.

Polygenic

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Nu

mb

er

of

Pe

op

le

Skin Color

Genetics of Blood Type

Try this one:

• Cross an O blood male with a Heterozygous A female

Fig. 23.18Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© Jane Burton/Bruce Coleman, Inc.

Genes Expressed due to Environmental Factors

F2generation

100%red-eye female

50% red-eye male50% white eye male

Discovery of sex linkage

P X

F1generation(hybrids)

100%red eye offspring

true-breeding white-eye male

true-breedingred-eye female

Genes on sex chromosomes• Y chromosome

– few genes other than SRY• sex-determining region• master regulator for maleness• turns on genes for production of male hormones

• X chromosome– other genes/traits beyond sex determination

• mutations:– hemophilia– Duchenne muscular dystrophy– color-blindness

• Sex-linked– usually means

“X-linked”– more than

60 diseases traced to genes on X chromosome

Duchenne muscular dystrophyBecker muscular dystrophy

Ichthyosis, X-linkedPlacental steroid sulfatase deficiencyKallmann syndromeChondrodysplasia punctata, X-linked recessive

HypophosphatemiaAicardi syndromeHypomagnesemia, X-linkedOcular albinismRetinoschisis

Adrenal hypoplasiaGlycerol kinase deficiency

Incontinentia pigmentiWiskott-Aldrich syndromeMenkes syndrome

Charcot-Marie-Tooth neuropathyChoroideremiaCleft palate, X-linkedSpastic paraplegia, X-linked, uncomplicatedDeafness with stapes fixation

PRPS-related gout

Lowe syndrome

Lesch-Nyhan syndromeHPRT-related gout

Hunter syndromeHemophilia BHemophilia AG6PD deficiency: favismDrug-sensitive anemiaChronic hemolytic anemiaManic-depressive illness, X-linkedColorblindness, (several forms)Dyskeratosis congenitaTKCR syndromeAdrenoleukodystrophyAdrenomyeloneuropathyEmery-Dreifuss muscular dystrophyDiabetes insipidus, renalMyotubular myopathy, X-linked

Androgen insensitivity

Chronic granulomatous diseaseRetinitis pigmentosa-3

Norrie diseaseRetinitis pigmentosa-2

Sideroblastic anemiaAarskog-Scott syndrome

PGK deficiency hemolytic anemia

Anhidrotic ectodermal dysplasia

AgammaglobulinemiaKennedy disease

Pelizaeus-Merzbacher diseaseAlport syndrome

Fabry disease

Albinism-deafness syndrome

Fragile-X syndrome

Immunodeficiency, X-linked,with hyper IgM

Lymphoproliferative syndrome

Ornithine transcarbamylase deficiency

Human X chromosome

Sex Linked Traits

• Usually carried on the X– Color blindness– Male pattern baldness (sex-influenced trait)– Hemophilia

Hemophilia

Hh x HHXHYXHXh

XHXh

XHY

Y

XH

sex-linked recessive

XHXH XHY

XHXhXhY

XH Ymale / sperm

XH

Xh

fem

ale

/ eg

gs

carrier disease

XH

Xh

Try this one:

• Cross a color blind male with a normal female