Genetic Inheritance

Inheriting genes

What is a Gene?

Genes are individualized sections of DNA on the chromosomes of cells. A gene in this context refers to the overall sequence that a trait may be pulled from.

What are Chromosomes and how many are in the Nuclei?

Chromosomes are strands of genetic material in the cell nuclei. There are 46 in total, or 23 pairs.

What purpose do Genes serve?

Genes carry instructions for making proteins that are involved in shaping how an organism looks and functions.

What is an Allele?

Alleles are different versions of a gene that determine an organism’s different traits.

What is a Genotype?

The genotype is an organism’s complete collection of alleles / complete genetic makeup.

What is a Phenotype?

The phenotype is all the traits you can observe in an organism.

How are expressed Traits determined?

Most traits arise from several different alleles interacting with each other, not just singular genes. Communication between cells and factors like the environment also affect the expression of traits.

What does Sexual Reproduction result in?

Sexual reproduction results in a unique mix of the parents’ genetic code in the offspring. An egg and sperm cell come together, each containing a set of each parents’ genes.

What are Patterns of Inheritance?

Patterns of Inheritance refers to the way traits pass from generation to generation.

What is Autosomal Dominance/Mendelian Inheritance? What is a simple example?

Autosomal Dominance refers to when a dominant allele completely overrides a recessive allele and gets expressed. The length of a cat’s fur is determined by a single gene called FGF5.

What does Heterozygous mean? What does Homozygous mean?

Heterozygous means two different alleles for the same gene (dominant/recessive). Homozygous means two matching alleles for a gene (dominant/dominant OR recessive/recessive).

What are Punnett Squares?

Punnett squares are the squares used to predict the genotypic and phenotypic ratios/probabilities of an offspring’s genetic traits.

What is Incomplete Dominance?

Incomplete dominance is when alleles blend together, leading to a mix of the expressed traits. Neither allele completely dominates the other, thus causing an intermediate phenotype.

What is Codominance?

Codominance is when traits linked to two different alleles show up separately on the organism’s phenotype; both alleles have traits that are fully expressed on the organism.

What is the best example for Multiple Allele inheritance?

The determination of a person’s blood type involves the presence of several different alleles (I^A, I^B, i).

What is Sex-linked Inheritance? What are the chromosomes associated with each sex?

Sex-linked inheritance is when a gene is carried on one of the chromosomes that also influences an organism’s sex. In many mammals, XX indicates a female, while XY indicates a male.

Why are Calico Cats an example of both Codominance and Sex-linked Inheritance?

In calico cats, the genes that code for fur color are found on the X chromosome. The codominant traits of a calico cat’s fur is often apparent on XX chromosomes, meaning nearly all calico cats are female.

What does Polygenic mean? What does Pleiotropic mean?

Polygenic traits are traits controlled by more than one gene. Pleiotropic traits are when one gene controls the expression of multiple traits.

What is Epistasis?

Epistasis is when the expression of one gene can influence or control the expression of another gene.

Why do Labradors come in 3 colors?

Labradors have a pigment gene expressing either black or brown fur, and then another gene that allows for the expression of pigment. Two recessive alleles on the second gene will inhibit the expression of pigment and lead to a yellow Labrador.

What are Complex/Quantitative traits? Why are they quantitative?

Complex traits are traits that are influenced by multiple genes and can also be heavily molded by the environment. These traits may fall on a spectrum that can be measured continuously, thus being quantitative.

Genetics can explain up to what percent of height differences in a population? How might the remaining percentage be determined?

~80% of height differences in a population can be explained through genetics. The remaining ~20% comes from environmental inputs, like nutrition or healthcare.

What percentage of our genome do we have in common with other humans?

99.9% of an individual’s genome is similar to other humans, meaning genetic differences may result from a measly 0.1%

Why is Genetic Predisposition important to understand?

Genetic predisposition for certain disease (like heart disease, diabetes, and cancer) increases the chances of developing those diseases, but doesn’t guarantee development.

What are Epigenetics?

Epigenetics are the way that life experiences can influence genetic instruction without editing DNA strands. These changes in genetic expression can be passed onto offspring.

What is Phenotypic Plasticity? How might honey bees show this concept?

Phenotypic plasticity is the idea that an organism’s phenotype may change within/throughout their lifetime. Female honey bees are fed royal jelly during youth, but only the continued consumption of royal jelly turns bees into queens. The rest of the female bees become sterile when switching to a beebread diet.

What is the difference between Monohybrid and Dihybrid crosses?

Monohybrid crosses often represent the probability of a single trait in an organism. Dihybrid crosses are used to show the probabilities of two distinct traits in an organism.

When mapping a dihybrid cross onto a Punnett square, what technique should be used to sort the alleles?

FOIL (first, outside, inside, last)

On what chromosome are sex-linked traits typically found? Where specifically are a male offspring’s X and Y chromosomes inherited from?

There are exceptions, but sex-linked traits are generally found on the X chromosome. Male children receive the X chromosome from the female parent and the Y chromosome from the male parent.

What are Pedigrees? What do the shape and shading designations mean?

Pedigrees are diagrams used to track a trait of interest throughout an organism’s family tree. Females are shown as circles, males are squares, and the shading represents organisms that have the trait of interest.

What are Autosomal Traits?

Autosomal traits are traits that are determined by genes on the autosomes (aka the 22 non-sex linked human chromosomes).

What is a Mutation?

A mutation is a change of genetic material, specifically a change within a nucleic acid (DNA, RNA, etc.).

What is an example of a Neutral or “Silent” Mutation?

The mRNA codon CUU codes for leucine; a certain mutation may change it to CUC, which still codes for leucine and results in no overall change.

Can an organism mutate at will?

Factors like chemicals, radiation, or certain events during DNA replication may make mutation more likely, but mutations are random and not purposefully inflicted.

What may happen in the 3 kinds of Gene Mutations?

Substitution may match incorrect bases. Insertion may add a base to a nucleic acid sequence. Deletion may remove a base from a sequence.

Why might Insertion and Deletion mutations be especially dangerous? What is this change in organization called?

Adding or removing bases from a sequence may change the format in which they’re meant to be read, therefore entire chains of incorrect polypeptides may be produced. This process is called a Frameshift Mutation.

What may happen in the 4 kinds of Chromosome Mutations?

Duplication may generate extra copies of genes on the chromosome. Deletion may break genetic material off the chromosome. Inversion takes a broken-off segment, inverses it, and returns it to the chromosome. Translocation takes a fragment from one chromosome and attaches it to a different chromosome.

What is Nondisjunction?

Meiosis allows for the creation of sperm/egg cells that contain half the number of chromosomes as the original organism. Nondisjunction is a result of the chromosomes not separating completely, leading to reproductive cells with too many or too few chromosomes.

How might mutations pass down to Offspring?

Asexually reproduced offspring may inherit the same mutation the parent cell has. A mutation may pass through sexual reproduction if the mutation is present in the sperm/egg cell.

What does the mutated hemoglobin gene do in a person with Sickle Cell disease? What might inheriting only one copy of the mutated gene do to a carrier?

The mutated shaped of the hemoglobin protein makes it difficult for red blood cells to carry oxygen, potentially leading to anemia. Carriers who only inherit one copy are asymptomatic and appear to have a protective factor against Malaria.