BiologyCards (copy)

Genetics

the study of heredity and genes

DNA: location, shape, chemical composition

location: is found in the nucleus of cells shape: is shaped as a double helix chemical composition: "deoxyribonucleic acid"

DNA composition

dna contains deoxyribose (5-carbon sugar) dna is a nucleic acid (molecule made up of nucleotides)

nucleotides have 3 parts: sugar, nitrogen base, phosphate

DNA structure

DNA: polymer Nucleotide: monomer

sugar-phosphate backbone

nitrogen base pairs

4 nitrogen bases in DNA

adenine, guanine, cytosine, thymine

DNA base pairing

dna is made of 2 chains of nucleotides connected by hydrogen bonds

Adenine (A) and Thymine (T) make 2

Guanine (G) and Cytosine (C) make 3

Chromosomes

threadlike structures found in nuclei of cells

each chromosome is 1 long dna molecule wrapped around proteins

chromosomes contain large numbers of genes among them, and the physical position of a gene is called a "Locus"

proteins

Nutrients the body uses to build and maintain its cells and tissues

RNA

ribonucleic acid sugar: ribose instead of thymine (T), RNA has uracil (U) forms of RNA include: Messenger RNA (mRNA) Transfer RNA (tRNA)

dna vs rna

deoxyribose sugar vs. ribose sugar, thymine vs. uracil , double strand vs. single strand

transcription

dna is unzipped at the desired gene (done by enzyme called helicase)

its copied by making a molecule of mRNA that complements 1 side of the dna strand

mRNA molecule can leave the nucleus to make a protein

translation

the copied mRNA leaves the nucleus and goes to a ribosome to make protein

the mRNA is read in sequences of 3 nucleotide bases (codons)

UAA, UAG, UGA in codon sequence means STOP

codons

each codon (mRNA readers) codes for an Amino acid.

as the mRNA is read more amino acids are joined together to form protein

somatic cells / body cells

• diploid (2n)

• contains 46 chromosomes (23 pairs)

• most cells in the body

sex cells / gametes

haploid cells contains 23, only 1 pair of each chromosome sperm and egg cells

somatic vs sex cells

somatic: diploid, 46 chromosomes, 23 pairs sex: haploid, 23 chromosomes, 1 of each

sex chromosomes

somatic cells have a pair of these, either XX (F) or XY(M)

autosomes (somatic chromosome)

all chromosomes except sex chromosomes somatic cells have 44 autosomes 22 pairs

homologuous chromosomes

Chromosomes that have the same sequence of genes and the same structure

Mitosis vs. Meiosis

Mitosis: one division forming 2 identical cells (clones) (somatic cells)

Meiosis: two divisions forming 4 genetically different cells (sex cells)

mitosis

1. duplicated chromosomes line up along the cell equator single file

2. the copies of the chromosomes then pull apart and go to opposite ends of the cell

3. the cell pinches inwards and makes 2 new identical cells

mitosis phases (4)

1. Prophase

• chromosomes condense and become visible

2. Metaphase

• chromosome lines up single file at the equator

3. Anaphase

• sister chromatids pulled apart to opposite ends of the cell

4. Telophase

• 2 new nuclei form around the 2 new sets chromosomes

cytokinesis: cell pinches inwards and splits into 2 new daughter cells

meiosis

• division of sex cells

• occurs in the testes and ovaries

• it divides diploid germ cells into haploid gametes

• daughter cells only have 23 chromosomes

meiosis divisions

first: the pair of chromosomes separate

second: the copied chromosomes separate like mitosis

fertilisation

fusion of a sperm and egg zygote = diploid, with 23 chromosomes from each parent, total of 46 zygote rapidly divides by mitosis to form an embryo

identical/non-identical twins

identical:

• zygote splits and forms 2 embryos

non identical:

• more than one egg is released and is fertilised

Gregor Mendel: peas

mendel grew pea plants and would keep detailed records of each plants different traits

he would breed certain plants together, taking notes on traits and traits of offspring

saw patterns in how traits were passed on

allele

Different forms/versions/combinations of a gene

e.g.: Gene: eye colour Alleles: brown, blue, green

Genotype

the combination of alleles genotypes are normally written as a letter per allele allele 1 - (b) allele 2 - (B)

Phenotype

the physical expression of a gene This is affected by the genotype and environmental factors e.g.: petal colour gene - purple petal

Heterozygous alleles

alleles are different (Bb)

Homozygous alleles

alleles are the same (BB), (Bb)

carriers

a carrier is one wo has the recessive heterozygote allele, but does not express it in their phenotype.

if 2 carriers have children, their offspring could:

• have the trait

• be a carrier

• not have the trait

dominance: alleles

one allele codes for a dominant phenotype and one codes for a recessive phenotype

if the allele for the dominant trait is in the genotype it's expressed in the phenotype

the allele for the recessive trait is ONLY expressed when it is the only allele present (bb)

Dominant vs. Recessive Alleles

Dominant: will always display in offspring- even heterozygous

Recessive: only displayed when homozygous recessive

punnett squares

A chart that shows all the possible combinations of alleles that can result from a genetic cross

genetic crosses

Where 2 organisms with specific traits are bred together and the traits of their offspring are recorded

co-dominance

in which both alleles of a gene contribute to the phenotype of the organism

mutations

errors or changes in the dna squence or an entire chromosome

they can lead to proteins not being made or producing different/non-functional proteins

causes of mutations

spontaneous mutation: the cause is unknown induced mutation: the cause (mutagen) can be identified

mutagen

factor that triggers mutations in cells examples: uv rays nuclear radiation x-rays certain chemicals some pathogens

types of point mutations

SUBSTITUTION of a different nucleotide DELETION of a nucleotide INVERSION of a small group nucleotides INSERTION of a nucleotide

consequences of point mutations (3)

silent: no change in amino acid used

missense: change in amino acid used

nonsense: no more amino acids added to the protein

chromosomal abnormalities: structural

DUPLICATION: part of the chromosome is duplicated DELETIONS: a portion of the chromosome is flipped around INVERSIONS: a segment of a chromosome is flipped around TRANSLOCATIONS: segments of two chromosomes are exchanged

chromosomal abnormalities: number

too many or too few chromosomes

this can be lethal and/or cause a genetic disorder

examples of beneficial mutations

• mutation that cause resistance to pesticides or antibiotics

• "heterozygote advantage": this is where having a copy of both alleles (the normal and mutated version) for a trait provides a survival advantage

passing on mutations

not all mutations can be inherited only mutations found in sex cells will be passed on to an offspring

what is a pedigree

a family record that shows how a trait is inherited over several generations

Trait Inheritance: autosomal

inheritance not connected to sex

trait inheritance: sex-linked

Y-linked trait only ever affect males

x-linked may affect one gender more than the other

4 types of inheritance

autosomal dominant autosomal recessive sex linked dominant sex linked recessive

Y-linked traits

type of sex-linked only ever affects males there's only ever 1 copy of the gene present and as such there isn't a need for dominant/recessive

genes

DNA segments that serve as the key functional units in hereditary transmission.

genome

the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes

genetic organisation of the cell

cell -> nucleus -> chromosome -> gene -> dna

haploid vs diploid

Haploid (23 chromosomes) means cell has one set of DNA, diploid has 2 sets and 46 chromosomes

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