Heredity EOC review

Unit Essential QuestionWhat are the principal mechanisms by which living

things reproduce and transmit hereditary information from parents to offspring?

• Mendelian genetics• Law of Segregation• Law of Independent Assortment• Punnett squares

• Meiosis• DNA

• Sugar – deoxyribose; Nitrogenous bases (A, T, G, C)• Complimentary base pairing• DNA replication

• RNA• Sugar – ribose; Nitrogenous bases (A, U, G, C)• Types of RNA (mRNA, tRNA, ribosomal RNA)

• Protein Synthesis• Transcription and Translation

• Genetic Engineering• Cloning, transgenic organisms, methods of genetic engineering (restriction enzymes, gel

electrophoresis, PCR)

DNA structure and replication

DNA – deoxyribonucleic acid

•Found in nucleus of eukaryotic cells. In the cytoplasm of prokaryotic cells.

•DNA is present to provide all the instructions the cells needs in order to perform. It codes for proteins which determine your traits (phenotype) and everything about you

DNA molecule

• Double helix “twisted ladder”• Made up of two strands of nucleotides• The bases of each nucleotide are held together by hydrogen bonds

(which break during replication)• A=T and G=C (Chargaff’s Rule)• Nitrogenous bases

• Adenine• Guanine• Thymine• Cytosine

Nucleotide

Process of DNA replication

• The twisted ladder unwinds• The hydrogen bonds breaks so that the two strands can separate from

one another (like unzipping a jacket)• Each strand acts as a template for the complementary strand

(following the rules of base pairing)• The new DNA strands each consists of an original strand and an old

strand

Process of DNA replication

Protein Synthesis

Proteins

• Made up chains of amino acids• A protein’s shape and function is determined by the combination and

arrangement of these amino acids.• Proteins are assembled on ribosomes (organelles found in the

cytoplasm)

DNA RNA

Double stranded (double helix)Stays in the nucleusContains bases A, T, C, and GLinear and in nucleus in eukaryotic cells, circular and in cytoplasm in prokaryotic cells

Single strandedUsed in the cytoplasmContains bases A, U, C, and GComes in 3 forms: mRNA, tRNA, rRNA

Types of RNA

mRNA: codes for amino acids. This is the “blueprint” or the set of instructions for building the proteinrRNA: reads the message on the mRNA strandtRNA: carries the amino acid to the site of proteins synthesis. Contains an anticodon that complements the mRNAstrand.

Transcription

• Occurs in the nucleus• DNA is transcribed into the mRNA strand• Remember that RNA contains uracil (U) instead of thymine (T)

Genetic Code: a chart that separates the codons into the amino acid that it codes for

Translation

• mRNA leaves nucleus and goes into cytoplasm• finds rRNA for the message to be read and translated• ribosome travels down mRNA strand until it finds AUG - the start codon• remember the strand is read 3 bases at a time• the tRNA with the anticodon (corresponding code)brings the correct

amino acid to the site to build a polypeptide chain (protein)• amino acids connect to the one before it and the process continues

until the rRNA reaches the end/stop codon on the mRNA strand (UAA, UAG, UGA)

Mendelian Genetics

• Purebred individuals (homozygous)• Have only one kind of gene for a trait

• Alleles• Variety of genes

• P generation (parental generation/parents)• F1 generation (first generation)

Homozygous Heterozygous

Pure Contains the same alleles, both are dominant or both are recessive (AA, aa)

Interbred Contains 2 different alleles (Aa)

Dominant Alleles Recessive Alleles

Use a capital letterAs long as the dominant allele is present, the organism will show that phenotype

Uses a lower case letterOrganism will only show the trait if a dominant allele is NOT present

•Law of Segregation•States that alleles are always divided so the offspring get one from each parent

•Punnett Square•Show all the possible combinations of alleles from a genetic cross

Genotype PhenotypeGenetic makeup of an organismBased on the gene combinationsExamples: BB, Bb, bb

Physical characteristics of an organismDetermined by its genotypeExamples: tall, short, yellow, blue

Monohybrid Cross Dihybrid CrossShows only one trait at a time Used to study the patterns of

inheritance of two traits at once

Law of Independent Assortment: Genes inherited for one trait does not affect which gene is inherited for another trait. In general, genes for different traits are not linked. So, when gametes are produced, the genes for traits found on different chromosomes separate independently.

Monohybrid cross

Dihybrid cross (remember to FOIL each of the parents)

Incomplete Dominance

• One allele is not completely dominant over another

Codominance

• Both alleles contribute to the phenotype

Multiple Alleles

• A gene that has more than one allele• Remember that in blood typing that

A and B are codominant.

Polygenic Traits

• A trait that is controlled by more than one gene• Provides a wide ranges of colors• Example: skin color, height, eye color

Chromosomes in humans

• Divided into two groups• Autosomes (pairs 1-22) determine most characteristicsexcept for gender• Sex Chromosomes (pair 23)

• Sex Chromosomes for males: XY• Sex Chromosomes for females: XX

Normal Female (XX) Karyotype

Sex-linked traits

• Determined by genes carried on a sex chromosome• Recessive sex-linked traits appear most often in males• Examples: color blindness, hemophilia

Monohybrid cross for sex-linked traits

Carrier mom

Normal dad

Normal female Carrier female

Normal male Affected male

Pedigree: a chart, family tree, used to trace the inheritance of a trait

Human GenesAutosomal recessive• Affects both sexes• Skip generations• Born to unaffected

parents

Autosomal Dominant (simple dominance)• Affects both sexes• DOES NOT skip

generations• Unaffected parents

will not transmit the trait

Copyright Pearson Prentice Hall

Human Genes

X linked recessive (sex-linked recessive)• More males than females affected• Skips generations• Never directly passed from father to son• All daughters of affected fathers are carriers

Copyright Pearson Prentice Hall

Meiosis and Genetic Variation

• Body cells are also known as somatic cells. They are diploid cells.• Body cells (somatic cells) divide through the process of mitosis• Sex cells are also known as gametes. These are haploid cells.• Sex cells (gametes) are produced through the process of meiosis• Diversity is caused by the crossing over process that occurs with the

homologous chromosomes during prophase 1 of meiosis. This creates variation within a population.

•Human gametes have 23 chromosomes (haploid)•Human somatic cells contain 46 chromosomes (diploid)

•Homologous chromosomes are chromosomes that have matching pairs of genes but may have different alleles

Mitosis Meiosis Makes new body cells that are diploidOne set of PMAT2 Daughter cells are genetically identical to the parent and to each other

Makes sperm and egg cells (gametes) that are haploid2 sets of PMAT (interphase only occurs once)4 daughter cells that are genetically different from each other and from their parent due to crossing over in prophase I

Nondisjunction

•Sometimes chromosomes fail to separate during meiosis and can cause disorders such as Down’s syndrome, Klinefelter’s syndrome, or Turner syndrome

Nondisjunction

Abnormal Karyotype (3 chromosomes on 21)as a result of nondisjunction

Mutations and Genetic Disorders

How are chromosomes and genes related• Gene is the segment of a chromosome that codes for a particular

trait.

What must occur before the cell divides?• Its chromosomes and DNA must replicate. This occurs during the S

phase of interphase.• If the DNA does not replicate correctly, this could lead to a mutation

or a change in a gene or chromosome.

Gene mutations Chromosomal mutations

mutations that occur in a single genePoint Mutationinvolve changes in one or a few nucleotidessubstitution - one base is changed into another. only affects a single amino acid. known as "silent" mutation.Frameshift Mutationscaused by point mutations: insertion (extra base is inserted) or deletions (a base is removed)whole reading frame is shifted and alters the code. as a result, this could alter what protein is made and may be unable to perform its normal functions.

changes in a chromosomal number or structure. Four types: a. deletion-loss of part of a chromosomeb. duplication-produce extra parts of a chromosomesc. inversion-reverse the direction of parts of a chromosomed. translocation-involves 2 chromosomes, a part breaks off of one and attaches to another

Gene mutations Chromosomal mutations

Somatic mutations Germ mutations

Mutations that occur in the body cellsNOT passed from parent to offspringCan dramatically affect an individual

Mutations that occur in gametesCan be passed from parents to offspring