AP Biology Unit 5: Heredity

Gametes

Gametes

Sex cells. These are the only types of human cells produced by meiosis, rather than mitosis

sexual reproduction

2 parents give rise to offspring that have uniquecombinations of genes inherited from the 2 parents

Clone

A group of genetically identical individuals from the same parent formed by asexual reproduction

Asexual reproduction

A single individual passes genes to its offspring without the fusion of gametes

Chromosomes

packaged DNA

Locus

a specific location of a gene on a certain chromosome

Heredity

The transmission of traits from one generation to the next

Genetics

The scientific study of heredity and variation

Genes

Units of heredity, and are made up of segments of DNA

Gametes (Sperm & eggs)

Genes are passed to the next generation via reproductive cells called

A karyotype

ordered display of the pairs of chromosomes from a cell

homologous or homologs

pairs of sister chromatids each pair comes from maternal and parental genes

haploid gametes

At sexual maturity, germ line cells in the ovaries and testes produce

Fertilization

The union of gametes (The sperm and the egg)

tetrad

group of four chromatids

Prophase l

Chromosomes condense, crossing over occurs.

synapsis

in prophase I, replicated homologs pair up and become physically connected along their lengths by a zipper-like protein structure, the synaptonemal complex,

metaphase l

tetrads line up at metaphase plate microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad

Telophase l

Each half of the cell has a haploid set of chromosomes; still consists of 2 sister chromatids. Cytokinesis usually occurs simultaneously, forming 2 haploid daughter cells

Anaphase l

pairs of homologous chromosomes separate. Sister chromatids remain attached at the centromere

Prophase ll

spindle apparatus forms chromosomes move toward the metaphase plate

Metaphase ll

Sister chromatids are arranged at the metaphase plate. Sister chromatids are no longer identical.

Anaphase ll

Sister chromatids separate. Sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles

Telophase ll

Chromosomes arrive at opposite poles. Nuclei form, chromosomes begin decondensing

Cytokinesis

Separates the cytoplasm

character

a heritable feature that varies among individuals (aka trait)

trait

A characteristic that an organism can pass on to its offspring through its genes. (aka character)

true-breeding

plants that produce offspring of the same variety when they self-pollinate

hybridization

mating or crossing of two different true-breeding varieties

P generation

the parental generation, true-breeding parents

F1 generation

the first filial generation, hybrid offspring from the P generation

F2 generation

the second filial generation, offspring from the self-pollination of the F1 generation

alleles

the alternative versions of a gene

dominant allele

the allele which determines the organism's appearance if two alleles at a locus differ

recessive allele

the allele which has no noticeable effect on the organism's appearance if two alleles at a locus differ

law of segregation

the two alleles for a heritable character segregate during gamete formation, ending up in different gametes

Punnett square

a diagrammatic device used for predicting allele composition of offspring from a cross between individuals of known genetic makeup

homozygous

a pair of identical alleles for a gene

heterozygous

two different alleles for a gene

phenotype

the observable trait from the genetic makeup

genotype

the genetic makeup of a trait

testcross

breeding an organism of unknown genotype with a recessive homozygote, revealing the genotype of said organism

monohybrid

A cross between individuals that involves one pair of contrasting traits

dihybrid

cross involving two traits

law of independent assortment

each pair of alleles segregates independently of each other pair of alleles during gamete formation

complete dominance

phenotypes of the heterozygote and dominant homozygote are indistinguishable

incomplete dominance

phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele

codominance

phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways

Tay-Sachs disease

an inherited disorder in humans when the brain cells cannot cannot metabolize certain lipids because a crucial enzyme does not work properly

pleiotropy

The ability of a single gene to have multiple phenotypic effects.

epistasis

a gene at one locus alters the phenotypic expression of a gene at a second locus

quantitative characters

a heritable feature that varies continuously over a range

polygenic inheritance

an additive effect of two or more genes on a single phenotypic character

multifactorial

many factors, both genetic and environmental, collectively influence phenotype

pedigree

family tree showing the occurrence of heritable characters in parents and offspring over multiple generations

carriers

heterozygotes that transmit the recessive allele to their offspring

cystic fibrosis

human genetic disorder caused by a recessive allele for a chloride channel protein

sickle-cell disease

human genetic disease caused by a recessive allele that results in the substitution of a single amino acid in a globin polypeptide that is part of the hemoglobin protein

Huntington's disease

a degenerative disease of the nervous system caused by a lethal dominant allele that has no obvious phenotypic effect until the individual is about 35-45 years old

The chromosome theory of inheritance

Genes have loci on chromosomes and chromosomes segregate and assort independently

Sex-linked gene

A gene located on a sex chromosome; can be X-linked or Y-linked

X-linked inheritence

X-linked genes are passed to daughters by both mother and father as females are XX. For males, only the mother provides the X-linked gene and the father provides the Y-linked gene as the mother only has X-linked genes and the father can only give Y-linked genes if the result is male progeny

Duchenne muscular dystrophy

Progressive weakening of muscles and loss of coordination

X-linked disorder: Hemophilia

Blood with an inability to clot normally

X-inactivation

During embryonic development of females, one of the X chromosomes (randomly chosen) is inactivated by methylation

Barr body

The inactive X chromosome of the developing female condenses into this and lies along the inside of the nuclear envelope

Linked genes

Located on the same chromosome and therefore tend to be inherited together during cell division

Genetic recombination

The production of offspring with a new combination of genes inherited from the parents

Parental type

A genetic cross that yields offspring with the same phenotype as one of the parents

Recombinants

A genetic cross that yields offspring with a different phenotype from either parent

Linkage map

A genetic map that is based on the percentage of crossover events

Map unit

Equal to a 1% recombination frequency. Map units are used to express relative distances along the chromosome

Nondisjunction

Occurs when the members of a pair of homologous chromosomes do not separate properly during meiosis I resulting in one gamete receiving two copies of a chromosome, while the other gamete receiving none

Aneuploidy

Fertilization of two gametes where one has an incorrect chromosomal number as a result of nondisjunction

Trisomic

Where the fertilized eggs receive three copies of the chromosome

Monosomic

Where the fertilized egg receives one copy of a chromosome

Polyploidy

The condition of having more than two complete sets of chromosomes

Deletion

Occurs when a chromosomal fragment is lost, resulting in chromosomes with missing genes

Duplication

Occurs when a chromosomal segment is repeated

Inversion

Occurs when a chromosomal fragment breaks off and reattaches to its original position backwards

Translocation

Occurs when the deleted chromosome fragment joins a nonhomologous chromosome

Down syndrome

An aneuploid condition that is the result of an extra chromosome 21 (trisomy 21). Down syndrome includes characteristic facial features, short stature, heart defects, and developmental delays

Klinefelter syndrome

An aneuploid condition in which a male possesses the sex chromosomes XXY (an extra X). Are sterile.

Turner syndrome

A monosomic condition in which the female only has one X. Sterile as their reproductive organs don't mature. Only known viable monosmy in humans.

Genomic imprinting

In mammals, the phenotypic effect of a gene may depend on which allele is inherited from each parent