SBI3U1 Unit 2: Genetic Processes

DNA

Deoxyribonucleic acid, fundamental molecule for life

Nitrogenous bases

The order of these

4, A, T, C, and G are what determine an organism’s traits.

Ribosomes

“Read” the order of nitrogenous bases in DNA to create proteins.

Chromosomes

A structure where DNA is carried for both prokaryotes and eukaryotes.

Plasmids

Prokaryotes and some protists contain plasmids which are small circular pieces of DNA that can be picked up or passed between cells.

Chromatin

Long unwound strands of DNA

How many chromosomes do humans have

Usually 46 in each cell

Genes

Sections of DNA

Locus

Location of gene in a chromosome

Functions of proteins

Directing development, muscle tissue, eye and hair pigment, hormones

Meiosis is

A form of nuclear division that results in 4 cells with half the number of chromosomes as the original parent cell

Meiosis location

Reproductive organs (ovaries, testes)

Karyotype

Collection of all of an individual’s chromosomes

Homologous pairs are organized

Paired based on size, shape, and function, offspring receive one of each pair from their biological parent.

Information in homologous pairs

The chromosomes in a pair are similar, but not identical. They contain the same genes, but the information in those genes may vary, for example different traits inherited from each parent.

Similarities of meiosis and mitosis

Cell growth, DNA replication, cell functions

Differences between meiosis and mitosis

Mitosis produces diploid cells and meiosis produces haploid gametes

Meiosis preparation

The cell must complete interphase, growing in G1, replicating its genetic material in S, and growing and preparing for division in G2

Chromatid

Strand of a chromosome

Centromere

Where sister chromatids join. Each chromosome has 1

#of cells in meiosis

Starts with 1, after meiosis 1 there are

2, after meiosis 2 there are 4

Gametes

Products of meiosis (haploid)

Haploid cells

One copy of each chromosome (non-homologous)

Diploid cells

2 copies of each chromosome (homologous, of maternal and paternal origin)

Crossing Over

During synapsis, sections of DNA are exchanged between homologous pairs. This is random and can happen up to 25 times, increasing genetic diversity.

Sex

Set of biological attributes in humans and animals

Testes

Typically begin producing testosterone at 9 weeks, furthering development of male characteristics

Hormones

Chemicals produced by special glands in the body and released into the bloodstream to send signals

Intersex

Umbrella term that describes bodies that fall out of the strict male/female binary

When can nondisjunction occur

Can occur in anaphase

Casgevy

CRISPR, a gene found in archaea/bacteria produced Cas9, which acts like “molecular scissors with a customizable targeting system.” We are all born with fetal hemoglobin but transition to adult hemoglobin shortly after birth. Researchers use Cas9 to turn off the adult hemoglobin gene and use the fetal hemoglobin gene.

Lyfgenia

Uses a lentivirus vector, a hollowed out virus used as an envelope or “molecular syringe which delivers a genetic shot right into cells.” In this case, the vector delivers a gene for an anti-sickling form of adult hemoglobin into the patient’s blood stem cells. It lacks the precision of CRISPR, though.

Allele

Different forms of a gene. They are located in the same position in each pair of homologous chromosomes

Dominant alleles

Determine the expression of genetic traits in offspring

Recessive alleles

Overruled by dominant alleles

Genotype

Genetic makeup of an organism

Phenotype

Describes how the genes are expressed

Incomplete dominance

Results in a mixture of two biological parent traits

Examples of incomplete dominance in humans

Known as polygenic traits, e.g. hair colour and texture, skin and eye colour, and height

Polygenic traits

Controlled by many different genes which primarily control the production of melanin, a pigment that leads to darker tones

Codominance

A pattern of inheritance where both versions of the allele are equally dominant, resulting in both traits showing up in the offspring

Heterozygous codominance

Both alleles will be expressed equally

Blood antigens

Antigens on red blood cells allow the body’s immune system to recognize and identify its own red blood cells. Different combinations of antigens determine blood type (commonly A and B)

ABO alleles

One blood type gene has 3 alleles, i (recessive) and IA and IB (codominant). Each individual has 2 alleles for blood type.

Blood antibodies

Blood contains antibodies that attack foreign blood types (e.g A blood contains B antibodies). They bond to foreign blood and cause cells to stick together.

Rhesus (RH) factor

Protein that is on the surface of some blood cells, expresses D antigen. Positive blood is presence of D antigen, negative blood is the absence.

Universal donor

Type O-

Universal recipient

Type AB+

Blood transfusions with incorrect blood type

Causes agglutination, systemic blood clumping, hemolysis, destruction of transfused blood, and/or death.

Rh pregnancy complications

When a pregnant person is Rh- and fetus is Rh+, they may produce Rh-antibodies if their baby’s blood comes in contact with theirs. This presents a risk for the next pregnancy if the antibodies reach an Rh+ fetus.

Rh immunoglobin

Stops the body from making Rh antibodies if it hasn’t already made them which can prevent severe fetal anemia in future pregnancy.

Pedigree chart

A family tree that shows patterns of inheritance for a single gene which tracks one single trait.

Pedigree symbols (sexes)

Square for male phenotypic sex, circle for female phenotypic sex, diamond for intersex/unknown. Coloured in means affected, blank means unaffected

Heterozygous

An organism with two different alleles

Homozygous dominant

An organism with 2 dominant alleles

Homozygous recessive

An organism with two recessive alleles

Hemizygous

An organism that only has one allele for a sex-linked trait (e.g someone with XY chromosomes will only have one allele for an X-linked trait)

Likelihood of red-green colourblindness in females vs. males

Colour blindness is an x-linked recessive trait, so a female (XX) would need to recessive alleles but a male (XY) would only need one recessive allele for the disorder, making it more common in males and those with Turner syndrome (XO)

Sex-linked traits

Sex chromosomes have genes for sex determination and some seemingly unrelated to sex development

What is the difference between X and Y chromosomes

Y chromosomes are smaller than X chromosomes and contain fewer genes.

Examples of sex-linked traits

Colourblindness, Duchenne Muscular Dystrophy

How can males receive alleles for x-linked traits

Only through the mother because the father passes on a Y chromosome

Why are tortoiseshell/calico cats almost always female?

Cat fur colour is determined by codominance and orange and black colours are both X-linked. For a calico coat they require both an orange and black allele, but a male can only receive one X-linked allele so they can only be orange or black, not both.

Autosomal trait

Trait located on one of the first 22 homologous chromosomes

Use of dihybrid crosses

Looks at the chances of offspring inheriting 2 different traits and are used for complete dominance inheritance patterns

Law of independent assortment

States that if genes are located on two separate chromosomes, they will be inherited independently of each other, resulting in four possible combinations of alleles

Definition of dihybrid cross

A cross between two individuals with 2 observed traits determined by 2 different genes to see the probability of the offspring inheriting 2 independent traits

Discontinuous variation

Expression of one gene has no effect on the expression of another

Continuous variation

The product of one gene is affected by the product of another (e.g. skin colour, height)

Nitrogenous base pairs

As pair with Ts, Cs pair with Gs meaning you can determine one strand of DNA based on the sequence of another (inverse)

Structure of DNA

A double helix with a backbone made of phosphate and sugar (deoxyribose) and rungs are nitrogenous bases

Nucleotide

Monomer/single unit of DNA made up of 1 deoxyribose molecule, 1 phosphate group, and 1 nitrogenous base

Central dogma of molecular biology

Every 3 nucleotides (codon) codes for 1 specific amino acid, which are components of proteins that determine traits

Protein shape

The order of amino acids (determined by DNA) determines the shape of the protein. Proteins perform all functions of life and a misshapen protein cannot carry out its function

Sickle cell disease

Caused by a mutation in both alleles of the gene that instructs the body to make hemoglobin and causes this protein to be misshapen, then bond together in red blood cells forming chains which cause RBCs to form sickles

Mutation definition

Change in the composition of a DNA molecule

Effects of mutations

Positive (provides advantages), no effect (changes DNA without changing coding regions), mildly negative (affects survival but not fatal/possibly fatal), negative (causes genetic disorder that may be fatal)

Spontaneous mutation definition

Caused by an error in DNA replication

Induced mutation definition

Caused by environmental agent (mutagen)

Mutagen

An environmental agent that alters the DNA sequence in a cell

Causes of spontaneous mutation

Caused by a DNA replication error (during S phase), e.g. incorrect base pairing by cellular proteins that carry out DNA replication

Physical mutagens

Causes physical change in DNA structure, e.g X-rays and UV radiation

Chemical mutagens

Molecule that enters the nucleus and causes a mutation by chemically reacting with the DNA, e.g. nitrates, gasoline fumes

Carcinogens

Chemical mutagens that can incorporate themselves into the DNA if they have a similar composition to the nucleotide and may cause incorrect nucleotides to be added during replication

Infectious agent mutagens

Viruses, bacteria, and protists which can cause types of cancer

Germline mutations

Mutations in gametes

Somatic mutations

In cells of the body

Chromosome mutations

Changes the structure of an individual chromosome, involving a long segment of DNA instead of just a nucleotide

Types of chromosomal mutations

Duplication, inversion, deletion, insertion, translocation

Chromosome duplication mutation

A section of a chromosome is repeated

Chromosome inversion mutation

When a segment of a chromosome breaks off and reattaches upside-down

Chromosome deletion mutation

Part of a chromosome is missing

Chromosome insertion mutation

Additional DNA is inserted into a chromosome

Chromosome translocation mutation

A piece of a chromosome breaks off and reattaches to another chromosome