Biology Module 4

Chromosome theory of inheritance

• states that all genes are located on chromosomes

• Each gene is a small region of the DNA molecule.

Gene

• the basic unit of information affecting a genetic trait

• Consists of a stretch of DNA coding for one protein on a chromosome

• what is the coding for?

Allele

• different versions of a given gene

• what is the code?

Mutation

• any change in the DNA sequence that makes up a gene

Locus

• The physical location of a gene on a chromosome

Heterozygous

• Two alleles at a locus are different

• consists of one dominant allele and one recessive allele.

• ex.) Pp

• Dominant allele is expressed

homozygous

• consists of two copies of the same allele

• Two alleles at a locus are identical

• can be dominant or recessive

• PP or pp

Homozygous dominant

• Consists of two copies of the dominant allele.

• The dominant allele is expressed.

• ex.) PP

homozygous recessive

• Consists of two copies of the recessive allele.

• This is the only way a recessive allele can be expressed.

• ex.) pp

sex-linked genes

• Together the genes located on these sex chromosomes make up the ____ _____ ______.

• if gene is located on X or Y chromosome

chromosomes

• a structure of nucleic acids and protein found in the nucleus

• carries genetic information in the form of genes

sex chromosomes

• at least one of the chromosomes carry a gene that determine the sex of an organism

• XX- Female

• XY- Male

• 1 chromosome

autosomes

• Eukaryotes carry two copies of each type of chromosome

  • together the two copies make up a pair of homologous chromosomes called _____.

• Every chromosome but sex chromosomes (1-22 chromosomes)

SRY gene

• triggers male development

• Y chromosome carries this

genetic carrier

• individuals who have only one copy of a recessive allele

• They can pass on the disorder allele.

  • do not have the disease.

• heterozygous trait

Cystic Fibrosis

• autosomal recessive allele disorder

• Affected individuals have two copies of that allele

• when a child inherits a recessive genetic disorder, both parents are heterozygous.

• ex.) Aa

dominant allele

• Capital letter

• Ex.) G

• the allele that is expressed when there are two copies of it

• expressed when there is one copy of it and one copy of the recessive variety.

• Expressed, Gg or GG

recessive allele

• Lower case letter

• Ex.) g

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

• ex.) expressed gg

phenotype

• physical expression of a gene(s)

  • What you can observe in an individual

genotype

• the alleles of the gene(s)

• The genetic information the individual carries

genetic trait

• inherited characteristics of an organism that can be observed or detected

  • i.e. inherited phenotypes

independent assortment of chromosomes

• Gregor Mendel

• the alleles (versions of genes) for different traits are distributed into gametes (sperm and egg cells) randomly and independently of each other during meiosis

• genes are independent of one another

• creates more genetic differences

crossing over

• is an exchange of segments of non-sister chromatids in prophase of meiosis

  • produces chromosomes with new combinations of alleles

• Creates more gene differences 

random fertilization

• creates more genetic differences 

• The sperm that fertilizes the egg is random

• the egg will receive a random combination of alleles

incomplete dominance

• produces an intermediate phenotype in the heterozygote

• when neither allele is able to exert its full effect

• ex.) Black rabbit + White rabbit = grey rabbit

  • all genes expressed in tandem

codominance

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

• ex.) Black cow + white cow = black + white spotted cow

  • both traits are expressed, but not mixed

  • think blood type

    • A + B= AB

complex traits

• are those that cannot be predicted using Mendel’s laws of inheritance

  • complex traits often display continuous variation in a population

  • ex.) kitten litter, there may be a black, brown, and white cat from same mother

Epistasis

• type of complex trait

• occurs when the phenotypic effect of a gene’s alleles depends on the presence of alleles for another, independently inherited gene

pleiotrophy

• The situation in which a single gene influences two or more distinctly different traits

• Albinism is an example

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

polygenic traits

• single traits controlled by more than one gene

  • In humans: hair, eye, and skin color

pedigree

• a chart similar to a family tree

• Shows genetic relationships among family members over two or more generations of a family’s medical history

• Provides scientists with a way to analyze information to learn about the inheritance of a particular genetic trait or disorder

deletion mutation

• occurs when a piece of a chromosome breaks off and is lost

inversion mutation

• occurs when a fragment of a chromosome breaks off and returns to the correct place on the original chromosome, but with the genetic loci in reverse order

translocation mutation

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

duplication mutation

• a chromosome becomes longer because it ends up with two copies of a particular chromosome fragment

• caused by unequal crossing-over during meiosis

Rh sensitivity

• After a Rh positive pregnancy, a Rh negative mother becomes sensitized to a Rh-positive baby.

• relates to the +/- part of your blood type

Gregor Mendel

• field of genetics originated in 1866 after ____ _____ published a paper on inheritance in pea plants

• work was adopted as the foundation for modern genetics