AP Bio - Unit 5 Heredity

What are homologous chromosomes?

Two chromosomes with the same set of genes, sometimes with different alleles

What is a gene?

basic unit of heredity and a sequence of nucleotides in DNA or RNA

What is an allele?

Different forms of a gene

Purpose of meiosis

produce gametes

Why in meiosis the chromosome number is halved?

Halves the sex cells in half, so that in fertilization, it will result in a normal amount of chromosomes (46 -> 23)

What is the end product of meiosis?

4 haploid cells

stages of meiosis in order

Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

What happens in meiosis I?

• Homologous chromosomes pair up

• Homologous chromosomes separates

• Two haploid cells are made with their sister chromatids still joined.

What happens in meiosis II?

• Sister chromatids separate

• 4 haploid daughter cells are formed

Significance of meiosis

Causes genetic variation

How is genetic variation achieved?

• crossing over

• independent assortment

• random fertilization

• mutations

What is crossing over?

exchange of genetic material between homologous chromosomes

How does crossing over contribute to genetic variation?

Crossing over creates new combinations of genes in the gametes that are not found in either parent

What is independent assortment ?

random separation of homologous chromosomes

How does independent assortment contribute to genetic variation?

each gamete ends up with a different set of DNA

• independent assortment affects which chromosomes end up in each cell

How does random fertilization contribute to genetic variation?

each parent to randomly contributes a unique set of genes to a zygote

What is a recessive allele?

A form of a gene that is not expressed when paired with a dominant allele

What is a dominant allele?

A form of a gene that is fully expressed, even when two different alleles are present

What is the law of segregation?

Parents pass on only one allele for each gene

What is the law of independent assortment?

during gamete formation, different pairs of alleles segregate independently of each other

• EX. which allele a gamete receives for gene A has no bearing of which allele a gamete receives for gene B

• ONLY DEALS WITH UNLINKED GENES

What are unlinked genes?

genes located on different chromosomes

What are linked genes?

genes located on the same chromosome that tend to be inherited together

What is a punnett square?

A chart that shows all the possible combinations of alleles that can result from a genetic cross

What is a dihybrid cross?

a cross that examines the inheritance of two different traits

What is the probability rule regarding multiplication?

Independent events that occur in a sequence; "AND"

What is the probability rule regarding addition?

Events not happening in a sequence; "OR"

What is incomplete dominance?

when one allele is not completely dominant over the other; blending of traits from parents (red+white=pink)

What is codominance?

both alleles contribute to the phenotype

How does the environment affect phenotype?

Exposure to certain things in the environment can affect gene expression and what phenotype is displayed.

What is a pedigree?

a chart that tracks which members of a family have a particular trait

What is autosomal recessive?

no skipping, many affect; two recessive needs to be present in order for the disease or trait to develop.

What is autosomal dominant?

Dominant in a trait that is not directly involved in determining sex; no skipping and many affected

What are sex-linked traits?

Traits controlled by genes located on sex chromosomes.

What is X-linked recessive?

mother/son and father/daughter links, skipping of gen

What is x linked dominant?

• Expressed in female in one copy

• More males affected

What is mitochondrial inheritance?

trait inherited from the moms and passes down to all kids

What is a genetic map?

ordered list of the genetic loci along a particular chromosome

What is nondisjunction?

Failure for chromosomes to separate properly.

What can nondisjunction lead to?

genetic abnormalities and chromosomal disorders

Name the 5 altercations of chromosome structure (mutations).

• deletion

• insertion

• duplication

• translocation

• inversion

What is a deletion mutation?

one nucleotide is taken away from a gene or DNA sequence

What is an insertion mutation?

The addition of a single nucleotide

What is a duplication mutation?

repeats a segment

What is an inversion mutation?

Reverses a segment within a chromosome

• BDE -> BED

What is a translocation mutation?

moves a segment from one chromosome to another, nonhomologous one

What type of chromosomal mutation is least disruptive?

point mutation because one base pair is exchanged and frame shift does not occur