AP Bio Unit 5 Heredity

Sexual Reproduction

Joining of egg and sperm

Karyotype

Picture of all an organisms chromosomes

XX Chromosome

Female

XY chromosomes

male

Gametes

Sex or reproductive cells (Egg and sperm cells)

Haploid

half or splitting, contrast to mitosis which completely splits into 46 and 46

Fertilization

Restores chromosome numbers, egg and sperm combine to make full 46

Zygote

fertilized combination of sex cells (46 chromosomes)

1st step of Meiosis

Duplication of DNA

Meiosis 1

1st division of meiosis separates homologous pairs, 2n=4single

Synapsis prohpase 1

pairing of homologous chromosomes

chiasmata

points where non-sister chromatids of homologous pairs connect and cross-over

The purpose of crossing over

ensure proper segregation during anaphase 1, exchange sections of chromosomes (swap), increases variation and new genetic variations

Meiosis 2

2nd division or meiosis separates sister chromatids

Value of sexual reproduction and genetic variation

independent assortment, crossing over, random fertilization

independent assortment

random alignment of homologous chromosomes in metaphase 1

Chromosomal differences

incorrect number of chromosomes or nondisjunction.

nondisjunction

homologous chromosomes don’t separation properly during meiosis, sister chromatids fail to separate during meiosis 2, too many or too few chromosomes

trisomy

form of nondisjunction, cells have 3 copies of a chromosome.

monosomy

form of nondisjunction, cells have only 1 copy of a chromosome.

Trisomy 21

form of down syndrome, 3 copies of chromosome 21, 1 in 700 children born in us

Frequency of down syndrome

correlates with the age of the mother

Chromosome 21

smallest human chromosome, still has severe efforts

Amniocentesis

A form of genetic testing in the 2nd trimester, sample of embryo cells, stain and photograph chromosomes

Sex chromosome abnormalities

human development more tolerant of wrong numbers in sex chromosome, but produces a variety of distinct syndromes in humans

Deletion

loss of a chromosomal segment

Duplication

Repeat a segment

inversion

reverses a segment

translocation

move a segment from one chromosome

Allele

trait that comes in alternative versions. At the same location on homologous chromosomes. EX: flower color, eye color

Recessive allele

Requires two copies to be seen, sometimes a missing or nonfunctional protein. EX: brown and blue eyes.

Genotype

Description of an organism’s genetic makeup. EX: letters, Bb, AA, bb

Heterozygous

Different alleles. EX: Pp, Aa

Law of Segregation

During meiosis, alleles segregate. Homologous chromosomes separate during meiosis 1.

Linked genes

If genes are on the same chromosome and come close together on it, they will usually be inherited together.

Dominant allele

Makes functional protein, masks other alleles. EX: Purple allele masks white

Phenotype

Description of an organism’s trait, the “physical”. EX: tall, curly hair, crooked teeth, a disorder.

Homozygous

Same Alleles. EX: aa, PP

Test cross

Used to determine unknown genotype. Breed the dominant phenotype (the unknown genotype) with a homozygous recessive.

Law of independent assortment

Different loci (genes) separate into gametes independently. Non-homologous chromosomes align independently. EX: Yellow and round don’t always go together.

Monohybrid cross

Inheritance of single trait. EX: flower color only, seed color only.

Dihybrid cross

Inheritance of 2 different traits. EX: seed color and shape.

Meiosis

2 divisions, daughter cells genetically different from parent, produces 4 cells, 2n to 1n, produces gametes, crossing over.

Mitosis

1 division, daughter cells genetically identical to parent cell, produces 2 cells, 2n to 2n, produces cells for growth and repair, no crossing over.