AP Bio: Unit 5 - Heredity

Segments of DNA that code for the basic units of heredity and are transmitted from one generation to the next

Reproductive cells that transmit genes form one generation to the next in animals and plants

The location of a gene on a chromosome

A single parent passes copies of all its genes to its offspring; New offspring arises by mitosis and has virtually exact copies of the parent’s genome

A group of genetically identical individuals

2 individuals contribute genes to the offspring; results in greater genetic variation in the offspring

All cells in the body that are not gametes; Has 46 chromosomes

Pairs of similar(not identical) chromosomes.; Each pair is inherited from each parent

A picture of an organism’s complete set of chromosomes

X and Y; XX(female), XY(male)

Nonsex chromosomes

Sperm and ova(eggs); Haploid cells

Contain half the number of chromosomes of somatic cells(23 chromosomes)

Meiosis and fertilization

Type of cell division that reduces the numbers of chromosomes

The combination of a sperm and an egg cell

A fertilized egg

2n

4 daughter cells

replication occurs, creating a copy of each chromosome. Each replicated chromosome has 2 identical sister chromatids

1st cellular division in meiosis; Starts with a diploid cell

• Chromosomes condense, sister chromatids are attached at their centromeres

• Synapsis occurs which forms a tetrad which aligns homologous chromosomes gene by gene

• Crossing over occurs

• Spindle poles move away from each other

• Nuclear envelope disappears

Joining of homologous chromosomes along their length

DNA form one homolog is cut and exchanged with an exact portion of DNA from the other homolog; Leads to an increase in genetic variation

Criscrossed regions; Holds the homologs together until anaphase 1

Homologous pairs of chromosomes are lined up at the metaphase plate

Homologous pairs separate and move toward the poles(moved by spindle apparatus); Sister chromatids stay connected

• Homologous chromosomes move until they reach the opposite poles

• Each of the 2 daughter cells contain a haploid(n) set of chromosomes

The maternal and paternal chromosome of each pair sort randomly; Increases in genetic variation

Second cellular division in meiosis; Begins with a haploid cell

A spindle apparatus forms and sister chromatids move toward metaphase plate

• Haploid # of chromosomes are now arrayed on the metaphase plate

• Sister chromatids aren’t identical due to crossing over

• Kinetochores of each sister chromatids are attached to microtubules from opposite poles

The centromeres of the sister chromatids separate and individual chromosomes move to opposite ends of the cell

• The chromosomes have moved all the way to opposite ends of the cell

• Nuclei reappears

• Each of the 4 daughter cells have haploid # of chromosomes and is genetically different from the other daughter cells and from the parent cell

In Metaphase 1, homologous chromosomes can pair up in any combination with any of the homologous pairs facing either pole; 50% change a daughter cells will get a maternal or paternal chromosome from each of the homologous pairs

Each combination of egg and sperm is unique since each egg and sperm is different

Parents in a genetic cross

Offspring of P generation

Offspring of F₁ generation

• Alternative versions of genes account for variations in inherited characteristics among offspring

• For each character, every sexually reproducing organism inherits 1 allele from each parent

• If the 2 alleles are different, then the dominant allele will be expressed in the offspring, whereas the recessive allele will have no noticeable effect on the offspring

• The 2 alleles for each character separate during gamete production

Alternative versions of the gene

The 2 alleles for each character separate during gamete production

Each pair of alleles will segregate independently during gamete formation

For 2 or more independent events, multiply the probabilities of each of the 2 events

For 2 or more mutually exclusive events, add together their individual probabilities

The heterozygote and the homozygote for the dominate allele are indistinguishable

F₁ hybrids have an appearance that is between that of the 2 parents

2 alleles are dominant and affect the phenotype in 2 different but equal ways

2 or more genes have an additive effect on a single character in the phenotype

Require 2 copies of the defective gene for the disorder to be expressed

Require only 1 copy of the allele in order for the disorder to be expressed

Genes have specific locations on chromosomes and that it is chromosomes that segregate and assort independently

Located on a sex chromosome

Located on the same chromosome; Tend to be inherited together during cell division

Production of offspring with a new combination of genes inherited from the parents

Occurs when the members of a pair of homologous chromosomes do not separate properly during Meiosis 1 or sister chromatids don’t separate properly during Meiosis 2