AP Bio Unit 5 Test

What does Meiosis produce?

genetically different haploid (one chromosome) cells

• aka: sperm and egg cells

diploid cell

a somatic cell containing two complete sets of chromosomes (23 pairs or 46 X’s)

• one chromosome inherited from each parent, forming homologous pairs

gametes

genetically different haploid cells

haploid cells

cells with a single set of unpaired chromosomes (23 individual X’s)

What does meiosis I produce?

2 haploid (23 single X) cells that will be further divided

what are somatic cells?

body cells

• 46 chromosomes

• 2 sets of each type

• produced by mitosis

• diploid cells (2n)

What are gametes?

sex cells

• 23 chromosomes

• 1 set of each type of chromosome

• produced by meiosis

• haploid cells(n)

what are homologous chromosomes?

A pair of chromosomes, one chromosome from each parent

What is synapsis?

the pairing of homologous chromosomes

What happens in interphase I before prophase I?

chromosomes duplicate (create the X)

What happens in prophase I?

• The homologous chromosomes pair up and exchange segments (synapsis)

What happens in metaphase I?

the 23 pairs (46 chromosomes) line up on the equator of the cell

What happens in anaphase I?

• The homologous pairs split up and are pulled to opposite poles

what happens in telophase I?

• meiotic spindle breaks down

• new nuclear envelope is formed

• cytokinesis

• cleavage

• two haploid daughter cells are formed (23 chromosomes → 23 X’s)

What is cytokinesis?

the cytoplasm divides into two

big differences between meiosis I and II

• no DNA Replication in interphase II

• no crossing over in prophase II

• independent assortment

• chromatids separate in anaphase II

• produces 4 non-identical, haploid daughter cells

How do meiosis and sexual reproduction produce genetic variation?

1. crossing over during prophase I

2. independent assortment during meta and anaphase

3. random fertilization

What is nondisjunction?

The failure of chromosomes or chromatids to separate normally during meiosis. Happens if:

• Both members of a homologous pair go to one pole in meiosis I

• both sister chromatids go to one pole meiosis II

Effect: gametes are no longer haploid

What does the law of independent assortment say?

What it says: Alleles for different genes (controlling different traits, like seed color and shape) are sorted and distributed to gametes independently of one another

• Result: Traits are inherited randomly and don't influence each other, as long as the genes are on different chromosomes

Explain the 3 steps of Mendel’s process

1. P generation: cross the parents (1 purple and 1 white)

2. Observe F1 Generation: all purple

3. cross F1 generation to produce F2: 3 purple 1 white

What are alleles?

the alternate versions of genes

how many versions of a gene does an organism inherit?

2, one from each parent

If 2 alleles differ(A vs a), which determines the organism’s appearance?

the dominant one (A)

What is Mendel’s law of segregation?

for any trait, a parent has two gene copies (alleles) but randomly passes only one of those alleles to each offspring in a sex cell (gamete)

• results: ensures genetic diversity

What is the gene, genotype, and phenotype and give an example

gene → general character trait (ex: plant height)

genotype → the inherited trait (ex: tall trait vs short trait)

phenotype → visible expression of the inherited trait based (ex: tall vs short plant)

What is heterozygous?

inheriting 2 different version of a gene → 1 dom and 1. rec (ex: Tt)

What is homozygous dominant?

inheriting 2 of the same dominant alleles (ex: TT)

What is homozygous recessive?

inheriting 2 of the same recessive alleles (ex: tt)

what is the probability scale

0 to 1

how do we determine the probability that two or more independent events will occur together in a specific combo?

multiplication rule → probability of 1 x probability of 2

how do we determine the probability one of two events will occur?

Addition rule → probability of 1 + probability of 2

What are Mendel’s 3 laws?

1. Law of Dominance

2. Law of Segregation

3. Law of Independent Assortment

What is the law of dominance?

What it says: In a heterozygote (Aa), the dominant allele (A) completely masks the effect of the recessive allele (a).

• Result: The observable trait (phenotype) will be the dominant one.

What are the 6 possibilities for a unexpected ratio?

• Incomplete and codominance

• gene linkage

• sex-linked genes

• polygenic traits and pleiotropy

• phenotypic plasticity

• non-nuclear inheritance

What is incomplete dominance?

When neither allele is completely dominant in a gene

• result: a blended hybrid phenotype

What is codominance?

When both alleles are dominant in a gene and expressed at the same time in different ways

• ex: human blood typing

What is gene linkage?

Genes that are adjacent and close to one another on the same chromosome appear to be genetically linked

• This probability can be used to calculate the distance between them → if less than 50%, the genes are likely linked

What is a genetic map?

an ordered list of genetic loci along a particular chromosome

What are sex-linked genes?

A single gene that is located on a sex chromosome

• there can be both x-linked and y-linked genes in humans

What is pleiotropy?

one gene has multiple seemingly unconnected phenotypic effects

What is epstasis?

expression of one gene impacts the expression of another

what are polygenic traits?

additive effect of 2+ genes on a single character

What is phenotypic plasticity?

Environmental factors can influence gene expression and lead to phenotypic plasticity

What is non-nuclear inheritance

maternally inherited genes

What is a null hypothesis?

That genes are unlinked and therefore there’s no statistical difference between observed and expected

When do you reject/fail to reject a hypothesis?

reject when: x² > the critical value (given by chart based on p-value) → genes are linked

fail to reject: x² < the critical value → genes are unlinked

Autosomal dominant

a genetic trait or disorder is passed on via a single mutated gene on a non-sex chromosome (autosome), requiring only one copy from one parent for someone to be affected

• in other words, the mutated gene is dominant (50% chance of being received)

autosomal recessive

a genetic trait or disorder appears only when a child inherits two mutated copies of a gene, one from each parent, both of whom are typically unaffected carriers

X-linked dominant

a gene causing a trait or disorder is on the X chromosome, and just one copy of that altered gene is enough to cause the condition in both males and females

X-linked recessive

A faulty gene on the X chromosome causes a trait or disorder, affecting males much more often because they only have one X, while females usually need two faulty copies (one from each parent) to be affected

• if disorder is passed from father to only daughters, it must be X-linked recessive