Unit 5 Heredity

Genes

segments of DNA that encode for proteins, which in turn affect how traits are expressed.

Alleles

versions of a gene, such as eye color being brown or blue.

traits

characteristics such as eye color and blood type.

Homologous Chromosomes

pairs of a chromosome, one from the father and one from the mother, in a diploid organism with the same genes at the same loci.

gametes

haploid sex cells (egg and sperm)

karyotype

a visual representation of an induvidual’s chromosomes.

Unique events to meiosis and phase they occur (3)

1. Crossing over - prophase 1

2. Lining Up of Homologous Pairs - metaphase 1

3. Separation of Homologous Pairs - anaphase 1

Prophase 1

Chromosomes condense, homologous chromosomes pair up and crossing over occurs at the chiasmata to make recombinants.

Metaphase 1

Homologous pairs align with random orientation at the cell’s equator.

Anaphase 1

Homologous chromosomes are separated and pulled to opposite poles of the cell.

Telophase 1

Two haploid cells form, each containing half the number of chromosomes.

PMAT II

same as mitosis, except for the uneven division of cytoplasm in eggs/polar bodies.

3 ways meiosis increases genetic variation

1. crossing over

2. independent assortment

3. random fertilization

Mendel’s discoverings (3)

1. Law of Segregation

2. Law of Independent Assortment

3. Dominant and Recessive Alleles

Law of Segregation

Each gamete carries only one allele for each gene so each individual has two alleles, one from each parent.

Law of Independent Assortment

Alleles for different genes segregate independently of each other during formation of gametes. (no linked traits)

genotype vs. phenotype

genotype - genetic makeup of an organism

phenotype - physical expression of genes

Monohybrid crosses

punnett squares that examines the inheritance of a single trait.

Dihybrid crosses

punnett squares/FOIL that examines the inheritance of two different traits at the same time.

Laws of Probability (2)

Multiplication rule - states that the probability of two or more independent events occurring together is the product of their individual probabilities. Ex.) chance of A 50% x chance of B 50% = chance of A and B 25%

Addition rule - used when calculating the probability of any one of multiple mutually exclusive events occurring. Ex.) chance of A 50% + chance of B 50% = chance of A or B 25%

Pedigree

shows relationships between family members and indicates which individuals express or carry a particular trait.

Autosomal Dominant (4)

The trait appears in every generation

Both males and females are equally likely to express the trait

affected individuals have at least one affected parent

unaffected individuals do not pass the trait to their offspring

Autosomal Recessive (4)

The trait can skip a generation

Both males and females are equally likely to express the trait

affected individuals can have unaffected parents - carriers

the trait often appears in siblings rather than in parents and children

X-linked Dominant (3)

The trait does not skip generations

Affected males pass the trait to all their daughters but not sons

affected females can pass the trait to both genders

X-linked Recessive (4)

The trait can skip generations

More males are affected than females

Affected males often have unaffected carrier mothers

Sons of affected males are not affected, and daughters are carriers

Y-linked (3)

The trait does not skip generations

Only males are affected

the trait is passed from affected fathers to all their sons.

Incomplete Dominance

neither allele is completely dominant, resulting in a phenotype that blends the two parent traits

Codominance

Both alleles are expressed equally in the phenotype

Multiple Alleles

many genes have more than two alleles. Ex.) Blood type A, B, and O

X inactivation

ensures that one functional copy of the X chromosome are in each body cell. leads to mosaicism, where cells express different alleles depending on which X chromosome is activated.

Linked Genes

Genes that are located close together on the same chromosome tend to be inherited together.

Linkage Maps

smaller percentage — closer the genes are and increased likelihood of recombining together as a unit

50% - max, no linkage

Non-nuclear DNA

DNA is also found in the mitochondria, inherited only from females in humans. Chloroplasts also have DNA.

phenotypic plasticity

the ability of a single genotype to produce different phenotypes based on environmental conditions

Tay-Sachs disease

a genetic disorder caused by a mutation in the HEXA gene, leading to the progressive degeneration of nerve cells

Sickle cell anemia

caused by a mutation in the HBB gene which results in the production of abnormal hemoglobin.

nondisjunction

when chromosomes fail to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes.

Down syndrome (trisomy 21)

caused by an extra copy of chromosome 21, leading to developmental and physical challenges

Turner syndrome

caused by complete or partial absence of one of the X chromosomes in females, results in short stature and infertility