Module 4 Terms bio

Polyploidy

when an organism has more than two complete sets of chromosomes

Humans normally have 2 sets of chromosomes → 2n

Common in plants

Genetic trait

inherited characteristics

Chromosome theory of inheritance

all genes are located on chromosomes

Each gene is a small region of the DNA molecule.

• Humans have an estimated 25,000 genes located on 23 pairs of chromosomes

 Single Trait/Monohybrid cross

looks at one trait at a time

Gene Two Trait/Dihybrid cross

looks at two different traits at the same time

Allele

Different versions of a given gene

• B = brown eyes

• b = blue eyes

Independent assortment of chromosomes

During meiosis, chromosomes are separated randomly and independently, so the alleles for different genes can end up in different combinations in the gametes (sex cells)

EX:If you have a chromosome carrying A/a and another carrying B/b, the gametes can get different combinations like AB, Ab, aB, or ab.

Mutation

Any change in the DNA sequence that makes up a gene

Crossing over

when matching chromosomes swap pieces of DNA with nonsister chromatids (identical) during meiosis I, creating new combinations of genes

Locus (loci)

the specific location of a gene on a chromosome

 Random fertilization

The sperm that fertilizes the egg is random

Therefore the egg will receive a random combination of alleles

Heterozygous

Two alleles at a locus are different

Incomplete dominance

when neither allele is able to exert its full effect

• Two traits blend

Homozygous

Two alleles at a locus are identical

Dominant and recessive

Codominance

when the effect of the two alleles is equally visible in the phenotype of the heterozygote

• Neither allele is diminished or diluted by the presence of the other all

Homozygous dominant

Two copies of the dominant allele

 Autosomal traits

traits controlled by genes located on the autosomes (non-sex chromosomes)

• EX: Brown vs. blue eye color is a trait influenced by genes on autosomes

Homozygous recessive

Two copies of the recessive allele

Pleiotropy

single gene influences two or more distinctly different traits

EX: Albinism is caused by a single recessive allele affecting pigment formation, but other traits such as vision are also affected

Sex-linked genes

Genes located on the sex chromosomes

X chromosome carries 1,180 gene loci

Y chromosome carries 60 gene loci

Polygenic traits

single traits controlled by more than one gene

Leads to a Range of Phenotypes in the Population

Chromosomes (Sex chromosomes vs Autosomes)

•Sex chromosomes - at least one of the chromosomes carry a gene(s) that determine the sex of an organism

• Autosomes are all other chromosomes

Epistasis

happens when one gene affects how another gene shows up

• EX:

  • One gene determines black vs. brown pigment.

  • Another gene determines whether that pigment is actually deposited in the fur.

  • If the second gene says, "don't deposit pigment," the dog will have yellow fur, even if it has the genes for black or brown pigment.

SRY gene

Determines the sex of an offspring

Y chromosome carries it, but can be found on the X in rare cases

Pedigree

chart similar to a family tree

Shows genetic relationships among family members

Genetic carrier 

People who have only one copy of a recessive allele

Can pass on the disorder

They don’t have the disease

Deletion mutation

Happens when a piece of a chromosome breaks off and is lost

Dominant allele

The allele that is expressed when there are two copies of it. Also, when there is just one copy of it and one copy of recessive allele

Capital letter

Inversion mutation

Happens when a fragment of a chromosome breaks off and returns to the correct place on the original chromosome, but the genetic information in reverse order

Recessive allele

The allele that is expressed only when there are two identical copies of it

Lower case letter

Translocation mutation

Happens when a broken piece from one chromosome becomes attached to a different, nonhomologous chromosome

Phenotype

Physical expression of a gene

• what can be observed in an individual

  • EX: hair color

Duplication mutation

A chromosomal abnormality in which a chromosome becomes longer because it has two copies of a particular chromosome fragment

Genotype

the alleles of the gene

• the genetic information that the person carries

  • EX: BB is the genotype for brown hair (phenotype).

Rh sensitivity

After an Rh- positive pregnancy, an Rh-negative mother becomes sensitized to a Rh-positive baby (creates antibodies)

If the woman becomes pregnant with another Rh- positive fetus, her anti-Rh antibodies will create a miscarriage