AP BIO: UNIT 5- HEREDITY

5\.1

Meiosis

Meiosis

• produces four haploid genetically different daughter cells

• Goes through two rounds of division instead of one

Prophase 1

• Homologous chromosomes pair up

• Chromatin condenses

• Crossing over occurs(increases genetic diversity)

• Spindle fibers move to opposite poles

Homologous chromosomes

Chromosomes that are the same size(one from mom and one from dad)

Recombinant Chromosomes

When non-sister chromatids exchange genetic information during crossing over they form recombinant chromosomes

Metaphase 1

Homologous chromosomes line up INDEPENDENTLY in the middle of the cell

Independent Assortment

* Homologous chromosomes randomly line up in the middle of the cell
* Increases genetic diversity since there are 8 million combinations in which the chromosomes can assort themselves

Anaphase 1

Homologous chromosomes separate and go to opposite poles

Telophase 1

• Cell spilts into two haploid cells

• Chromatin de condenses

• Spindle fibers come back to the middle of the cell

Prophase 2

• Chromatin condenses

• Sister chromatids pair up

• NO crossing over

Metaphase 2

Sister chromatids line up in the middle of the cell

Anaphase 2

Sister chromatids move to opposite poles

Telophase 2

• Produces 4 haploid cells

• Chromatin de condenses

• Nuclear envelope forms

Interphase

G1: cell growth

S: DNA replication

G2: prep for division

Meiosis by the number

Before Interphase: 46 chromosomes

After Interphase: 92 chromosomes

After Meiosis 1: 46 chromosomes

After Meiosis 2: 23 chromosomes

Fertilization will occur meaning 23 + 23 = 46 chromosomes

5\.2

Meiosis and Genetic Variation

How does crossing over increase genetic diveristy

• The non-sister chromatids exchange genetic information and become recombinant chromosomes

• Increase genetic diversity by exchanging information

How does independent assortment increase genetic diversity?

• Random assortment of chromosomes on the metaphase plate leads to 2^23 combinations of genetic code

• This increases genetic diversity because there are so many combinations

How does random fertilization increase genetic diversity?

• Any sperm can fuse with any egg

• This increases genetic diversity because each the sperm and the egg have so many genetic combinations and can fuse randomly(in total 70 trillion combinations)

5\.3

Mendelian Genetics

What substances show common ancestry?

• DNA/RNA

• Ribosomes

The ribosomes can code for the same polypeptide chains. A human insulin gene can be inserted into a prokaryote

• Go through glycolysis and can generate ATP (same metabolic processes)

Law of Segregation

Chromosomes separate during anaphase

Complete Dominance

As long as the individual has at least 1 dominant allele it will completely mask the recessive allele

Incomplete Dominance

No allele is completely dominant over the other; the phenotypes blend together

Ex: Red snapdragon x white snapdragon = pink snapdragon

Co-dominance

No allele is completely dominant over the other; the phenotypes exist together as their own entity

Ex: AB Blood. Individual will have

5\.4

Non-Mendelian Genetics

Linked Genes

• Genes that are on the same chromosome and inherited together

• Less likely to separated during crossing over

Sex-linked traits

Genes located on sex chromosomes

Map Distance

• How close linked genes are to one another

• Can be determined by how often a pair of genes participates in crossing over

• Linked genes have a recombination frequency of less than 50%

Map Distance Example

• Linked genes have a recombination frequency of 5% they are very close together(low chance of being separated)

• They are 5 map units apart

• Linked genes that have a recombination frequency of 30% are further apart(slightly higher chance of being separated)

• They are 30 map units apart

Sex linked traits and alleles

• Most sex-linked traits are on the X chromosome because it is longer

• Alleles are represented by a superscript

• Females can be heterozygous for a trait because they have two X chromosomes but it is impossible for a male to be heterozygous because they have only 1 X chromosome

Autosomal Dominant vs Recessive

Autosomal = # of males affected = # of females affected \n Dominant = every generation is affected(P, F1, F2 so on) \n Recessive = unaffected parents can have affected offspring

Sex linked Dominant vs Recessive

Sex Linked = affects one gender more than the other \n Dominant = # of females affected > # of males affected \n Recessive = # of males affected > # females affected

Many traits are the product of multiple genes

Hair color is determined by multiple genes

Non-nuclear inheritance

• Traits not inherited from the nucleus

• Mitochondria and chloroplasts include a non-nuclear genome

• Mitochondria and chloroplasts traits are maternally inherited(sent to egg/ovule)

• In animals affected females will affect ALL their offspring but affected males won’t

• Nuclear traits are inherited both paternally and maternally

5\.5

Environmental Effects on Phenotype

Phenotypic Plasticity

• One genotype can produce multiple phenotypes

• Due to environmental factors(organism can have the same genes but different appearance- based on environment)

Ex: Hydrangea plants can produce different colors based on soil pH

5\.6

Chromosomal Inheritance

How does law of segregation lead to more genetic diversity

• Alleles are separated during anaphase

• This increase genetic diversity because it allows for daughter cells to have more varied options for alleles

Mutation Alleles

• Laws of segregation and independent assortment explain why mutation can be anywhere

• A mutation allele can manifest a genetic disorder if the allele is harmful

Nondisjunction

• Failure of chromosomes to separate during gamete formation

• Sex cells either have too few or too many chromosomes

Gene transmission

• Parents pass on genes from themselves to their offspring

• Mutations can occur in offspring even if they are not in the parent