Biology Exam 3

Ch. 13-17

meiosis

produces cells with half the chromosomes of the parent cells, occurring only in specialized cells

meiosis II

when do sister chromatids separate in meiosis?

meiosis I

When do homologs separate during meiosis?

fertilization

unites sperm and egg, re-establishing pairs of homologous chromosomes, with both maternal and paternal genes

heredity

transmission of traits from one generation to the next

variation

demonstrated by difference in appearance that offspring show from parents and siblings

genes

units of heredity, made up of segments of DNA

locus

gene’s specific position along chromosome

gamates

genes passed to the next generation via reproductive cells

23 chromosomes

How many chromosomes do human gamates have?

46 chromosomes

How many chromosomes do humans have in somatic cells?

asexual reproduction

single individual passes all genes to offspring without fusion of gamates

clone

group of genetically identical individuals from same parent

sexual reproduction

two parents give rise to offspring that have unique combination of genes inherited from the parent

life cycle

generation to generation sequence of stages in reproductive history of an organism

23 PAIRS of chromosomes

How many pairs of chromosomes do human somatic cells have?

homologous chromosome

2 chromosome in each pair

true

Chromosomes in homologous pair are same in length and shape (T/F)

diploid cell (2n)

two sets of chromosomes

haploid cell (n)

gamete contains single set of chromosomes

4 daughter cells

How many daughter cells result in two cell divisions of meiosis?

-synapsis and crossing over prophase I

-homologous pairs at metaphase plate

-separation of homologs during anaphase I

What are 3 events in meiosis I?

mutations

changes in organism’s DNA, original source of genetic diversity

alleles

different version of genes from mutations

genetic variation

resulting of alleles during sexual reproduction

2ⁿ

number of combinations possible when chromosomes assort independently into gamates

adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)

random fertilization

Mitosis conserves chromosome sets, producing cells genetically identical to parent cell. Meiosis reduces chromosome sets, from diploid to haploid, producing cells that differ genetically from each other and from parent cell.

Difference between mitosis and meiosis?

Genetics studies heredity, which is how genes located at a specific locus on chromosomes are transmitted through gametes, and variation

Relation between heredity, variation, genetics, genes, locus, and gametes?

-each parent cell has two alleles for each character, and the two alleles separate during gamete formation

-offspring inherit one allele from each parent

-when offspring reproduces, alleles separate

How are traits transmitted from parent to offspring?

Mendel

discovered basic principles of heredity by breeding garden peas

character

heritable feature that varies among individuals

trait

each varient for character

true-breeding

produce offspring of same variety when they self pollinate

hybridization

mate two contrasting, true-breeding varieties

P generation

parents

F₁ generation

hybrid offspring of P generation

F₂ generation

F₁ individuals self-pollinate or cross pollinate

1) Alternative version of genes

2) Two alleles per Character

3) Dominant and Recessive Alleles

4) Law of Segregation

Mendel’s model of inheritance in four steps:

first step of Mendel’s model

-alleles, different versions of genes

-locus, each gene resides at specific location on specific chromosome

second step of Mendel’s mondel

-homozygous (AA or aa) - two alleles at locus may be identical

-heterozygous (Aa) - two alleles at locus may differ

third step of Mendel’s model

-Dominant - determines organism’s appearance

-Recessive - no noticeable effect on appearance

fourth step of Mendel’s model

-law of segregation

-egg or sperm gets on of two alleles

-segregation of alleles corresponds to distribution of homologous chromosomes to different gametes in meiosis

Law of Segregation

two alleles for a heritable character separate during gamete formation and end up in different gametes.

Punnett Square

possible combination of sperm and egg

dominant allele

Capital letter

Recessive allele

Lowercase letter

phenotype

visible or otherwise measurable physical or biochemical characteristic of organism

genotype

particular pair of alleles present for any gene

testcross

breeding mystery individual with homozygous recessive individual

Homozygous dominant or heterozygous

Individual with dominant phenotype could be what?

heterozygous

If the offspring displays recessive phenotype, then the mystery parent must be what?

dihybrids

crossing two true breeding parents differing in two characters

dihybrid cross

cross between F₁ dihybrids, determine whether two character are transmitted to offspring as package or independently

Law of Independence Assortment

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

-alleles aren’t completely dominant or recessive

=gene has more than two alleles

-gene produces multiple phenotype

Inheritance of characters deviate from Mendelian patterns due to…

complete dominance

phenotype of heterozygote and dominant homozygote are identical

incomplete dominance

phenotype of F₁ hybrids is between phenotype of two parental varieties

codominance

two dominant alleles affect the phenotype in separate, distinguishable ways

pleiotropy

most genes have multiple phenotypic effects

epistasis

expression of a gene at one locus alter phenotype expression of a gene at a second locus

Quantitative characters

those that vary in population among a continuum

polygenic inheritance

additive effect of two or more genes on a single phenotype (ex: height, 180 genes affect height)

-generation time too long

-parents produce few offspring

-breeding experiments are unacceptable

Why are humans not good subjects for genetic research?

recessively inherited disorders

show up only in individuals homozygous for allele

carriers

heterozygous individuals who carry recessive allele, but are phenotypically normal

albinism

recessive condition characterized by lack of pigmentation in skin and hair

Dominant alleles

What cause human disorders?

achondroplasia

form a dwarfism caused by rare dominant allele

Huntington’s Disease

degenerative disease of nervous system

Genes are located on chromosomes

What is the relationship between genes and chromosomes?

drosophila melanogaster

species of fruit fly

-produce many offspring

-generation can. be bred every two weeks

-four pairs of chromosomes

Why are fruit flies conveinent for genetic studies?

wild type

normal phenotypes common in fly populations

mutant phenotype

traits alternative to wild type

large X and small Y chromosome

2 types of sex chromosomes that humans and other mammals have:

female

person with 2 X chromosome

male

person with 1 X and 1 Y chromosome

sex determining region on Y (SRY)

gene on Y chromosome, responsible for development of tasks in an embryo

sex linked gene

gene located on either sex chromosome

Y linked gene

genes on Y chromosome, 78 genes

X-linked genes

genes on X chromosome, 1,100 genes

-color blindness

-Duchenne muscular dystrophy

-hemophilia

-male pattern baldness

Disorders caused by recessive alleles on X chromosomes

linked genes

genes located on same chromosome tend to be inherited togethter

genetic recombination

production of offspring with combinations of traits differing from either parent

parental types

offspring with phenotype matching one parental phenotypes

recombinant types

offspring with nonparental phenotypes (new combination of traits)

nondisjunction

pairs of homologous chromosomes or chromatids don’t separate normally during meiosis

aneupoidy

results from fertilization of gametes in which nonjurisdctioin occur

monosomic

zygote has 1 copy of chromosome

trisomic

zygot has 3 copies of chromosome

down syndrome

aneuploid condition that results from three copies of chromosome 21

klinefelter syndrome

result of extra X chromosome in male, producing XXY individuals

turner syndrome

monosomy X, produces X0 females who are sterile

polyploidy

organism has more than 2 complete sets of chromosomes

triploidy (3n)

3 sets of chromosomes

tetraploidy (4n)

4 sets of chromosomes

-deletion

-duplication

-inversion

-translocation

4 changes in chromosome structure due to breakage of chromosome?

syndrome cri du chat

results from specific deletion in chromosome S

CML

caused by translocation of chromosomes