AP Bio Unit 5

Diploid

2n; has two homologous chromosomes for each number

Homologous chromosomes

same genes, different alleles

Haploid

n; has only one chromosome for each number

Gene locus

physical location of a gene on a chromosome

Synapsis

association of homologous chromosomes where small sections cross over

Genetic recombination

how genetic information is exchanged between chromosomes during synapsis/crossing over, resulting in completely new chromosomes

Independent assortment

all chromosome pairs line up independently of one another, creating lots of biological diversity; happens during metaphase I

Nondisjunction

the failure of chromosomes/chromatids to correctly separate during cell division; in meiosis, leads to formation of gametes with irregular number of chromosomes (and zygotes with irregular chromosome numbers)

Trisomy

2n+1; when a zygote has three copies of one chromosome; trisomy in the 21st chromosome leads to down syndrome

Monosomy

2n-1; when a zygote only has one copy of a chromosome; monosomy in the X chromosome leads to turner syndrome, where a female has only one X chromosome (males would die)

Polyploidy

3n/4n; product of a diploid gamete and a haploid/diploid gamete; common among plants, typically lethal in animals

Order of genotypic/phenotypic ratio (only one gene)

Homozygous dominant : heterozygous : heterozygous recessive

Order of phenotypic ratio (two genes)

Dominant x2 : Dominant/recessive : Recessive/dominant : Recessive x2

Mendel’s Law of Segregation

The two different alleles from one parent get separated into different gametes, so the offspring has the chance of inheriting either one, but only one

Phenotypic ratio of a dihybrid cross between two heterozygotes

9:3:3:1

Linked genes

Two genes located close together on the same chromosome; because of this, they are often inherited together, causing mostly parental type offspring

Parental type offspring

Offspring who have the exact same phenotype for specific traits as one of their parents

Recombinant type offspring

Offsprings who mix phenotypes of both of their parents

Autosomal dominant trait + pedigree

A normal trait (from chromosome 1-22) that is dominant

Autosomal recessive trait + pedigree

A normal trait (from chromosome 1-22) that is recessive

X-linked trait

A trait linked to the X chromosome; aka sex-linked chromosome

X-linked dominant trait + pedigree

An X-linked trait that is dominant - affects mostly women because women get two X chromosomes but only need one dominant X-linked allele to show the trait

X-linked recessive trait + pedigree

An X-linked trait that is recessive - affects mostly men because men get only one of their mother’s X chromosomes, meaning they need only one X-linked recessive allele to show the trait

Strategies to figure out inheritance pattern from a pedigree

• See if sexes are disproportionately affected and if they are, which one (shows autosomal vs x-linked dominant vs x-linked recessive )

• See if unaffected parents can produce an affected offspring (if they can, it is autosomal recessive and both parents must be heterozygous)

Mitochondrial Inheritance Pattern

Genes inherited solely from mitochondrial DNA; follows a maternal line because you get all mitochondria from your mom

Incomplete dominance

One allele is dominant, but not completely; heterozygotes have a blend of both alleles in phenotype

Codominance

Both alleles are dominant; heterozygotes show both distinct alleles in phenotype

Blood type inheritance pattern

Basic blood type A/B/O has three genes: I^A, I^B, and i

• IA and IB are codominant, and both are dominant over i

• Each combination has a different phenotype

A-type blood

• A antigens

• Anti-B antibodies

B-type blood

• B antigens

• Anti-A antibodies

AB-type blood

• A and B antigens

• No antibodies (because they would attack the blood cell antigens)

O-type blood

• No antigens

• Anti-A and anti-B antibodies (will not attack blood cells because they have no antigens)

Universal recipient

AB blood; because it has both types of antigens, it will be familiar to all antibodies in all other blood types

Universal donor

O blood; because it has no antigens, it will not be attacked by any antibodies

Rh factor gene

Determines if blood type is positive or negative; follows Mendelian patterns when positive is dominant (R) and negative is recessive (r)

Epistasis

When phenotypic expression of a gene is altered by another, separate gene (in the example, the baldness gene is epistatic to the hair color gene)

Polygenic inheritance

When multiple genes influence a phenotype (a bell curve in a population is indicative of this)

Nature vs. Nurture

Phenotype depends on genotype as well as environment

Wild type

Phenotype most commonly found in natural populations, shown by w+ (often dominant trait but not necessarily)

XY system

Sex chromosome system where XX = female, XY = male (ex. humans)

X-0 system

Sex chromosome system where XX = female, X = male (absence of second chromosome; ex. grasshoppers)

ZW system

Sex chromosome system where ZW = female, ZZ = male (ex. many birds)

Haplo-diploid system

Sex chromosome system where females are diploid (“normal” development) and males are haploid (formed from single unfertilized eggs through mitosis)

SRY gene

A gene on the Y chromosome that causes one to be biologically male; when it crosses over to the X chromosome it can cause XX males, and when it is mutated, it can cause XY females (both very rare)

Deletion (and duplication)

When a chromosomal fragment is lost (may be attached to another chromosome, producing a duplication)

Inversion

Chromosomal fragment is reversed

Translocation

Fragment of a chromosome joins a nonhomologous chromosome

X-inactivation in Female Mammals

One X chromosome is inactivated in females because they have 2, and only need one; each cell will inactivate a different X chromosome, and all cells that descend from that cell will have the same inactivated X

Barr body

Inactivated X chromosome in female mammals that appears dark because it is still in condensed chromosome form