AP Bio Unit 5 (2)

Genetics

Study of heredity

Heredity

How traits are passed from parents to offspring

Traits

Characteristics someone possesses (eye color, hair color, height, etc)

Gene

Segments of DNA that encode for proteins, and proteins express the trait

Alleles

Versions of a gene

Asexual reproduction

When an organism produces offspring that are genetically identical to the parent cell

Sexual reproduction

When two parents come together and produce an offspring with a combination of traits from both parents. This contributes to genetic diversity

Homologus chromosomes

Pairs of chromosomes in a diploid organism

What is the structure of homologous chromosome pairs?

Each pair has the same genes at the same loci, however they may contain different alleles

Loci

The specific, fixed physical location gene on a chromosome

Somatic cells

All body cells expect sex cells

Diploid

two sets of chromosomes

Gametes

The reproductive cells (sperm and egg cells)

Haploid

only one set of chromosomes

Autosomes

The courses that don't determine the sex of an organism

Sex chromosomes

The chromosomes that determine an individual's sex

Karyotype

A visual representation of an individual's chromosomes

Purpose of a karyotype

Used to look for chromosomal abnormalities, to determine the number and structure of chromosomes, arranged from largest to smallest, sex chromosomes are identified separately

Fertilization

The union of a sperm and egg cell that forms a zygote

Meiosis

Type of cell division that reduces the chromosomes by half producing four genetically different gamete (PMAT occurs twice)

Mitosis vs. Meiosis

Occurs in somatic cells

Only undergoes one division

Results in two genetically identical daughter cells

Meiosis vs mitosis

Occurs in gametes

Undergoes two divisions

Results in four genetically different daughter cells

Crossing over

Occurs during prophase 1

Homologous chromosomes exchange segments of DNA

Creates new combinations of genes which increased genetic diversity

Chismata

where crossing over happens

Synapsis

the pairing of homologous chromosomes during meiosis

Lining up of homologous pairs (in meiosis)

Occurs in metaphase 1

The homologous chromosomes line up in pairs at the metaphase plate

Speration of homologous pairs (in meiosis)

Occurs in anaphase 1

Homologous chromosomes are pulled towards opposite poles of the cell

This reduces the chromosome number by a half

What type of cell do you have after meiosis 1?

Haploid

What does nondisjunction result in during meiosis?

the cell will no longer be haploid

What are two events that occur during meiosis that increase genetic diversity?

Crossing over and sexual reproduction (random fertilization)

Random fertilization

Any sperm can fertilize any egg

Genetic diversity

The measure of variability among individuals within a single species (Represented by the variation of alleles in the gene pool)

Mutation

Change the DNA sequences result from errors during DNA replication

What is the original source for new alleles?

Mutations

What occurs during sexual reproduction in terms of genetic diversity?

individuals can have different allele combinations for each gene

What happens when there is a loss of genetic diversity?

makes species unable to successfully reproduce and they are less adaptable to changing environment

What populations are more susceptible to genetic diversity?

Small populations

What causes a loss of genetic variety?

Inbreeding and genetic drift

Genetic drift

When genetic composition of a population fluctuates randomly over time

Independent assortment

During meiosis chromosomes line up randomly and each new cell gets a mix of chromosomes from mom and dad

Where does independent assortment occur?

In metaphase 1

Mendel's Law of independent assortment

Different traits are passed down from parent to offspring independently of each other

Heterozygous

An organism that has two different alleles for a trait

Homozygous

An organism that has two identical alleles for a trait

P generation

First generation that comes together to produce an offspring

F1 Generation

Comes directly from the parental (P) generation

F2 Generation

Comes crossing two F1 generations

Law of Segregation

Every organism has two alleles for a trait, but during the process of meiosis, these two alleles separate, resulting in 1 allele per gamete. Then the gametes combine giving the offspring two alleles--one from each parent

Where does segregation occur?

anaphase 1

Law of Dominance

The dominant allele will mask the expression of the recessive allele, resulting in the dominant allele being expressed as the organism’s phenotype

Law of Independent Assortment

States that different traits are passed down from parent to offspring independently of each other

What are the only genes the law of independent assortment applies to?

Genes located on different chromosomes and that are very far apart on the same chromosome

Dominant Alleles

It only takes one dominant allele for the trait to be expressed, so the combination of alleles can be either heterozygous or homozygous (Represent by capital letter)

Recessive Alleles

In order for a recessive allele to be expressed, there must be a homozygous combination of the recessive allele (Represented by lowercase letters)

Genotype

The genetic makeup of an organism

Phenotype

The physical expression of that genotype

Punnet Squares

Based on Mendel's principles of genetics and is used to predict the genotype and phenotype of an offspring

monohybrid cross

focuses on one trait being expressed

What's the genotypic ratio in a monohybrid cross between 2 heterozygotes?

1:2:1

What's the phenotypic ratio in a monohybrid cross between 2 heterozygotes?

3:1

dihybrid cross

 focuses on multiple alleles, and predicts the probability of them appearing together

Before performing the cross, what must occur first?

The FOILing of the genotypes

What's the phenotypic ratio in a dihybrid cross between 2 heterozygotes?

9:3:3:1

Multiplication rule

The probability of two or more independent events occurring together is the product of their individual probabilities

Addition rule

Calculates the probability of any one of multiple mutually exclusive events occurring

Pedigree

A chart for an individual to see if they will pass a genetic disease down to their children

Carriers

A parent that does not express the trait but has an allele for the trait

Autosomal Dominant

Only 1 dominant allele needed

Affects males and females equally

Appears in every generation

Autosomal Recessive

Needs two recessive alleles

Can skip generations

Parents are often carrier

X-linked Recessive

Gene on X chromosomes

Males are affected more

Females are usually carriers

Passes from carrier mother to son

X-linked Dominant

Only 1 dominant allele on X needed

Affects both sexes, but females more

Affected father means all daughters will be affected

Y-linked

Found on the Y chromosomes

Only males are affected

Passed from fathers to all their sons

Does not skip generations

Mapping distance

Shows the frequency of recombination between linked genes

Linkage maps

Show the relative positions of genes on a chromosome

What does a smaller recombinant frequency mean?

The closer the genes are

What parent is nonuclear DNA inherited from?

The mother

Imcomplete dominance

Situation in which one allele is not completely dominant over another allele resulting in a blend of BOTH alleles

Codominance

A condition in which both alleles for a gene are fully expressed in some type of pattern

multiple alleles

When a gene has MORE than two possible versions (alleles)

How many alleles will an offspring inherit from their parents if there's multiple alleles

2, 1 from each parent

polygenic inheritance

When the phenotype of an organism is controlled by multiple GENES

How can you tell there's polygenic inheritance?

When there's a wide range of phenotypes

Linked genes

Genes located on the same chromosome that tend to be inherited together in genetic crosses.

Sex-linked traits

Traits that are controlled by genes found on the sex chromosomes (X or Y)

What sex chromosome is larger?

X chromosome

Which gender is more likely to show sex-linked disorder?

Males because they only have one X so unlike females there isn't another allele (X) to cover it if the trait is recessive

X Activation

In women, one of the X chromosomes in each cell in inactivated

What's the purpose of X activation?

ensuring that females don't have twice as many X-chromosome gene products as males

Barr body

Deactivated X chromosome

Mosaicism

Where different cells express different alleles depending on which X chromosome is inactive

What is the impact of environmental factors on traits?

Environmental factors help determine what genes are turned on and off

Phenotype Plasticity

The ability of a single genotype to produce different phenotypes depending on environmental conditions

Where do genetic disorders come from?

Mutations in specific genes

Chromosomal Disorders

Occur due to abnormalities in the number or structure of the chromosomes

Nondisjunction

When chromosomes fail to separate properly in meiosis

Wild type

the normal type (no mutation)

Epistasis

The phenotypic expression of one gene affects the phenotypic expression of another gene

In epistasis, what are the genes like?

Genes are NOT independent, but they interact to produce phenotypes

Pleiotropy

One gene affects multiple phenotypic characteristics

What are pleiotropic alleles responsible for?

Multiple symptoms of hereditary diseases