AP Bio - Unit 5

Autosomes

Autosomes

Chromosomes 1-22

Chromosome 23

Sex chromosone, xy for male or xx for female

Diploid cell

2 sets of each chromosone (2n)

Ex: body cells

Haploid cell

1 set of every chromosome

Ex: gametes, egg/sperm cells

Prophase I

Chromosomes wind together at the centromere, pairs find each other

Homologous chromosomes

2 seperate single chromosomes that code for a similar trait, but are different genetically

Crossover

At Prophase I, homologus chromosomes find each other, trade DNA with the other pair, creating genetic diversity

Metaphase I

Homologus pairs line up across the center of the cell (the order they’re in also can cause genetic diversity)

Anaphase I

Homologus pairs are pulled apart

Telaphase I

Nucleus reenvelopes the chromosomes, resulting in cells with 23 chromosomes and 46 chromatids

Prophase 2

The chromatin again winds into chromosomes

Metaphase 2

Single file chromosomes line up down the middle of the nucleus

Anaphase 2

Sister chromatids are split apart

Telaphase 2

Nucleus splits apart, resulting in 4 genetically unique cells with 23 chromosomes and no chromatids (all single chromosomes)

Alleles

Variation of a gene - in every chromosome, there are 2 alleles (one from each parent) that determine a trait

Dominant allele

Represented by a capital letter, only needs one present to be the phenotype (ex: AA, Aa)

Recessive allele

Represented by a lowercase letter, needs two present to be the phenotype (ex: aa)

A gene is made of….

2 alleles

Classic ratio of a monohybrid cross

1:2:1

Heterozygous gene

Has one of each allele type (ex: Aa)

Homozygous gene

Has two of the same allele type (ex: AA/aa)

Heterozygous dihybrid cross ratio

9:3:3:1

Test cross

Recessive genotype (ex: aa) tested with an unknown genotype.

Test cross result if the unknown genotype is dominant homozygous (AA)

All of the offspring will show the dominant trait

Test cross result if the unknown genotype is heterozygous (Aa)

Some of the offspring will show the recessive trait

Complete dominance

Dominant trait overpowers the recessive trait if it’s present in an allele

Incomplete dominance

Heterozygous form is a blend of the alleles (ex: homozygous red and white flowers will make heterozygous pink offspring)

Codominance

Heterozygous form equally expresses each allele (ex: homozygous brown and white cows would make a heterozygous brown and white cow)

Parent cross in the classic heterozygous dihybrid cross

GgRr x GgRr

Parent cross and F1 cross in the classic monohybrid cross

yy x YY, then all Yy

Sex linked trait

Traits determined by genes on sex chromosomes

Sex linked traits are..

Usually carried by females

Alleles of sex traits are represented with..

A superscript on the X or Y chromosome

Which organelles also give DNA besides the nucleus?

Mitochondria and chloroplasts

Mitochondrial and chloroplast DNA is from the _____

Female

Linked genes

Genes on the same chromosome

Linked genes are ______ to be inherited together

More likely

Relationship between map units and chances of crossing over

Less map units (closer together) - lesser chance of crossing over

More map units (further away) - greater chance of crossing over

The expression of polygenic traits is usually…

Bell shaped; there are usually more common combinations of alleles

Alleles for type A blood

AA, AO

Alleles for type B blood

BB, BO

Alleles for type AB blood

AB

Alleles for type O blood

OO

Autosomal recessive traits

Unaffected parents (carriers), affected offspring

Autosomal dominant traits

Affected parents, affected offspring

Sex- linked recessive traits

Affects males more than females

Sex linked dominant traits

Affects females more than males

Nondisjunction

Either homologous chromosomes not separating properly during Meiosis I or sister chromatids not separating properly during Meiosis II

Chromosomal defect - deletion

Chromosomal fragment is lost, resulting in a chromosome with missing genes

Chromosomal defect - duplication

A chromosomal segment is repeated

Chromosomal defect - inversion

Chromosomal fragment breaks off, but reattaches backwards

Chromosomal defect - translocation

Deleted chromosome fragment joins a non-homologous chromosome into a homologous one