HL Biology Unit 3 Inheritance

What is a Gene?

A heritable section of DNA that codes for one polypeptide

What is a Locus?

The specific spot on a chromosome that a gene occupies

What are Alleles?

Different versions of a gene

How are genes EXPRESSED?

Translation and Transcription

What is a Genome?

ALL of the genetic information of an organism

What is a Proteome?

ALL of the proteins that could be made in an organism

What are Base Substitution Mutations?

A change in nitrogenous bases within a gene that could lead to abnormal phenotypes

What is an example of a disease caused by a Base Substitution Mutation?

Sickle Cell Disease, where hemoglobin molecules change shape and can’t hold as much oxygen as needed in red blood cells

What are 4 differences between Prokaryotic and Eukaryotic Chromosomes?

Prokaryotic

• No histones on DNA

• Only one chromosome

• Circular DNA

• May have additional plasmid DNA

Eukaryotic

• Histones on DNA

• Multiple Chromosomes (46 in Humans)

• Linear DNA

• No plasmids

What is Conjugation?

When plasmids are transferred between bacterial cells to create genetic diversity despite reproducing asexually

What are Histones?

Proteins that DNA coils around to be packaged, usually there are 8 histones that are held together by a histone protein

What is a Nucleosome?

The structure that forms when DNA is coiled around histones

What is Linker DNA?

DNA that links nucleosomes together

What are Homologous Chromosomes?

Chromosomes that have the same sequence of genes, but not necessarily the same alleles for each gene

Why are Sister Chromatids NOT Homologous Chromosomes?

Not only do they have the same sequence of genes, but they also MUST have the same alleles for each gene

What are Haploid Nuclei?

Nuclei that only contain one copy of each type of chromosome (one set of chromosomes)

What are Diploid Nuclei?

Nuclei that have pairs of homologous chromosomes (two sets of chromosomes, one from each parent)

What can Chromosome Number be used to determine?

Chromosome # may help to set species apart from one another.

different #s cause failure in pairing → offspring would not have homologous chromosomes and therefore could not reproduce → organisms with different amounts of chromosomes would be unlikely to interbreed

What are Karyograms?

Diagrams that show homologous pairs of chromosomes in decreasing length (and gene banding patterns + centromere position)

What are Autosomes?

Chromosomes that do not code for the sex of an individual (XX/XY)

Where are Sex Chromosomes located in a karyogram?

At the end

What are two ways to get samples of Karyotyping?

Amniocentesis: Fetal cells are collected from the amniotic fluid

Chorionic Villi Sampling: Tissue samples are taken from the embryonic portion of the placenta

What can Karyotyping determine?

• Chromosome #

• Chromosomal Abnormalities (ex. trisomy)

• Biological sex

What can Karyotyping NOT determine?

• Genetic mutations

• Diseases caused by mutations

• Gender (social construct)

What does it mean for Meiosis to be a Reduction Division?

The number of chromosomes decreases: parent cell (46) → gametes (23)

What is Nondisjunction?

When cells receive not enough/too many chromosomes because…

-Anaphase 1: Both chromosomes of a homologous pair go to one pole, causing a failure of separation

-Anaphase 2: Both sister chromatids go to one pole, causing a failure of separation

What kinds of cells undergo Meiosis vs. Mitosis?

Germinal Cells (precursors to gametes) undergo meiosis, Somatic (body) Cells undergo mitosis

What is Independent Orientation?

When each chromosome aligns randomly and independently at the cell equator during Metaphase 1 of meiosis → yields independent assortment in Anaphase 1+2

What is the formula used to calculate the number of possible gamete combinations/phenotypes between two parents?

2ⁿ, n = # of chromosome pairs (23 in humans)

Why does age affect the likelihood of trisomy 21?

Oocytes that are stored for longer have a higher chance of mutating, since oocytes are stored for decades before being released and they may eventually experience mutations

What is Crossing Over?

A process where homologous chromosomes exchange genetic information by physically swapping sections of chromatids

What are Bivalents?

A pair of homologous chromosomes that form by synapsis, where they pair up in Prophase 1

What is a Chiasmata?

The point of contact between two sister chromatids during crossing over

What is Phenylketonuria (PKU)?

A disorder inherited by a recessive allele that causes phenylalanine to build up in the body, which is due to a change in the Phenylalanine Hydroxylase gene (PAH).

What is the difference between a Monohybrid and Dihybrid cross?

Crossing one trait vs. Crossing two traits

What is Phenotypic Plasticity?

The capacity to develop traits suited to an organism’s environment by varying patterns of gene expression, which can be reversed

What is Codominance? What is an example?

When both inherited alleles are seen in the phenotype simultaneously - Blood Types

What is Incomplete Dominance? What is an example and how do we write the alleles in notation?

When heterozygotes have an intermediate phenotype instead of showing just one allele - the Four O’ Clock Marvel, notation is R¹R²

What are Pedigrees?

Charts that show one trait’s inheritance through multiple generations, where males are represented by squares and females are represented by circles

What is Hemophilia? How is it written in a punnett square?

A sex-linked recessive allele that causes a failure in blood clotting - X^HY^h

What is Discrete/Discontinuous Variation? What is an example?

A pattern of inheritance where traits are clearly distinguishable and limited - PKU

What is Continuous Variation? What is an example?

A pattern of inheritance where traits are not clearly distinguishable and there is a range of possibilities - Height and Skin Pigmentation

What does it mean that Continuous Variation is often polygenetic?

The traits that show continuous variation are often controlled by multiple genes, that may also be influenced by environmental factors like diet

What are the 7 different parts of a Box and Whisker Plot?

Minimum, Maximum, Median, Quartile 1, Quartile 3, Range, Interquartile Range

What does it mean for a Box and Whisker plot to be Right-Skewed, Left-Skewed, or Symmetrical?

Right-Skewed: The median is closer to Q1 (most of the data is on the right)

Left-Skewed: The median is closer to Q3 (most of the data is on the left)

Symmetrical: The data is evenly distributed and the median is near the middle

How do you find lower and upper range outliers?

Lower Range: Any values < Q1 value - (1.5 * Interquartile Range)

Lower Range: Any values > Q3 value + (1.5 * Interquartile Range)

What is a Dihybrid Test Cross?

When a heterozygote with an unknown genotype is crossed with a homozygote parent - the genotypes of the children help find the unknown genotype of the heterozygous parent

List the 3 Mendelian Ratios for autosomal linked genes

Heterozygote (both traits) x Heterozygote - 9:3:3:1

Heterozygote (both traits) x Homozygote - 1:1:1:1

Heterozygous for one trait x Homozygote - 1:1:1:0

What are Linked Genes?

Genes located on the same chromosome that will be inherited together because they are close together - this is called being in the same linkage group

What is a Recombinant?

A new combination of alleles on a chromosome that can occur from crossing over - are usually the genotypes that have the smallest amount in a set

Describe how the number of chromosomes change through meiosis

43 → 23 per cell, with two cells in PMAT1 → 23 per cell, with four cells in PMAT2