AP BIO Unit 5

Gamete

haploid reproductive cell or sex cell (sperm, pollen grain, or egg)

Zygote

Fusion of the gametes gives rise to a fertilized egg cell, or zygote.

Haploid

cell, nucleus, or organism containing one set of chromosomes (n)

Diploid

cell, nucleus, or organism containing two sets of chromosomes (2n)

Meiosis I

first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid

Meiosis II

second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells

Crossing Over

exchange of genetic material between non-sister chromatids resulting in chromosomes that incorporate genes from both parents of the organism

Chiasmata/chiasma

a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.

How does meiosis increase genetic diversity?

• crossing over (P1)

• independent assortment (M1)

• fertilization

• mutations

How does crossing over/recombination increase genetic diversity?

Homologous chromosomes exchange segments of DNA in prophase 1. This creates new chromosome combinations with a mix of alleles from both parents.

How does independent assortment increase genetic diversity?

During metaphase 1, the homologous chromosomes line up randomly, creating over 8 million possible results.

How does fertilization of gametes increase genetic diversity?

The random fusion of any one sperm with any one egg further increases genetic diversity.

Law of Segregation

paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors

Law of Independent Assortment

genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur

Genotype

underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism

Phenotype

observable traits expressed by an organism

P Generation

parental generation in a cross

F₁ Generation

first filial generation in a cross; the offspring of the parental generation

F₂ Generation

second filial generation produced when F1 individuals are self-crossed or fertilized with each other

How to determine probability if A and B are mutually exclusive?

Sum rule

P ( X ) + P ( Y ) ‍

OR

How to determine probability if A and B are independent?

Product rule

P ( X ) ⋅ P ( Y ) ‍

AND

Incomplete dominance

in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype

Codominance

in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic

Multiple alleles

the many different versions of an allele present in a population

Pleiotrpy

the production by a single gene of two or more apparently unrelated effects (phenotypic traits)

sex linkage

genes on either the X or Y chromosome (23rd chromosome)

mitochondrial DNA

Circular DNA located within the mitochondria of a cell. Only inherited from the mother.

Map Distance

the relative distance between two genes on a chromosome

Phenotypic plasticity

the property of organisms to produce distinct phenotypes in response to environmental conditions

How can the environment influence gene expression?

Through epigenetic modifications. External factors such as temperature can chemically alter the DNA structure and thereby impacting an organism’s traits.

Nondisjunction

failure of synapsed homologs to completely separate and migrate to separate poles during the first cell division of meiosis

causes trisomy or monosomy and increases with maternal age

If it happened in M1, 100% are abnormal. If it happened in M2, 50% are abnormal.

Trisomy 21

Down’s Syndrome

Monosomy X

Turner’s Syndrome

XXY

Klinefelter’s Syndrome

5p deletion

Cri Du Chat

chi-square

1. Calculate chi-square

2. Find critical value

   • Degrees of freedom= categories - 1

   • P-value 0.05 if not specified

If chi-square is > critical value = reject

If chi-square is < critical value = fail to reject

mutagens

a physical or chemical agent that can cause a permanent change in the genetic material, usually DNA, leading to mutations (mutagenesis), not reversible

• Physical: heat, radiation; breaks the phosphodiesterase bonds in DNA

• Chemical: base-analog, base-modifying; often mimic a base and bonds in its place

• Biological: bacteria, viruses; increase the chance of cancer

epigenetics

the study of how behaviors and environments affect the way genes are expressed, heritable changes that do not involve changes in the DNA sequence, most are reversible

Ex. identical twins

autosomal traits

on somatic chromosomes (pedigrees)

autosomal dominant

• appears in males and females with same frequency

• affected offspring must have an affected parent

• rarely skips a generation

• if one parent is heterozygous ~50% of offspring will be affected

• Ex. Huntington’s Disease

autosomal recessive

• appears in males and females with same frequency

• affected offspring usually have an unaffected parent

• often skips a generation

• if both parents are heterozygous ~25% of offspring will be affected

• Ex. Cystic fibrosis

x-linked dominant

• appears more often in females than males

• affected sons must have an affected mother

• affected fathers will pass the trait to all their daughters

• hard to say it’s 100% x-linked

• Ex. fragile X syndrome

x-linked recessive

• appears more often in males than females

• affected sons must have an unaffected mother

• all daughters of affected fathers are carriers

• hard to say it’s 100% x-linked

• Ex. red green color blindness

mitochondrial inheritance

• trait comes from the mother only

• all children are at risk of being affected/carrier

• Ex. Leber’s hereditary optic neuropathy

linked genes

genes located near each other on the same chromosome and are often inherited together

some gametes are only possible with crossing over

actual outcomes for recombinant phenotypes is less than 25%/25%, and is statistically different than the expected outcome

locus (plural loci)

position of a gene on a chromosome

unlinked genes

genes located on separate chromosomes or more than 50 map units apart

all gametes are equally possible (with or without crossing over), consistent with the Law of Independent Assortment

actual outcome (phenotypic ratio) is not statistically different from the expected outcome (each 25%)

recombinant phenotypes

the results of crossing over, different from the parental phenotypes

recombinant frequency

total percentage of recombinants

map units apart on a chromosome

higher recombination frequency = higher occurrence of crossing over = greater distance apart

polygenics

phenotypic characteristic caused by two or more genes, can also be influenced by environmental factors

Ex. hair color, skin color, height

non-nuclear inheritance

occurs when genetic material (DNA) in the cytoplasm is inherited; often from the mitochondria or chloroplasts of only the female parent

bacterial conjugation

bacteria exchange genes, sex pilus is a projection that initiates contact between bacterial cells

plasmids

small circular DNA molecules, can move between bacterial cells during conjugation

test cross

used to determine the unknown genotype of an individual by crossing the unknown parent with a homozygous recessive individual to observe the phenotypes of the offspring

Heterozygous Dihybrid Cross

AaBb x AaBb

9 - dominant traits

3 - dominant, recessive

3 - recessive, dominant

1 - recessive traits

epistasis

a gene at one locus alters the effects of a gene at another locus

polygenic inheritance

phenotypic characteristic caused by two or more genes

X inactivation

condensation of X chromosomes through a process called methylation into Barr bodies during embryonic development in females to compensate for the double genetic dose

linkage map

a diagrammatic representation of the relative positions of genes or genetic markers on a chromosome, determined by their recombination frequencies during meiosis

polyploid

individual with an incorrect number of chromosome sets

gametes with extra chromosomes

deletion

a portion of a chromosome is lost or removed

duplication

a segment of a chromosome is copied, resulting in multiple copies of that segment

inversion

a segment of a chromosome is flipped or reversed, and then reinserted into the same location

translocation

a piece of one chromosome breaks off and attaches to another chromosome