Genetics

Where is DNA stored?

nucleus of a plant or animal cell

What does DNA determine

• How an organism develops

• How the parts of an organism function

DNA provides instructions for how _____ _____ join together to form _______

amino acids, proteins

Describe the structure of DNA

• very long, thin molecule made of thousands of atoms

• consists of two chains that twist around each other, AKA a double helix

• like a ladder. each rung is made up of two smaller molecules, AKA bases

Name the base pairs

A - T, C - G

what does a nucleotide consist of?

base, sugar, phosphate

How many chromosomes in a human body cell?

23 pairs

what are chromosomes?

long threads of DNA and are located in the nucleus of every cell

different patterns of bases form…

genes

what do genes determine?

• how an organism develops from an individual cell to an adult

• what nutrients are made in the body

• the types of enzymes produced

• how an organism looks and behaves

protein synthesis

process used by the body to make proteins

transcription

occurs in the nucleus. mRNA transcribes (copies) DNA. Thymine is substituted for Uracil in mRNA (T→U)

translation

mRNA strand is read 3 bases at a time in order to make protein. These bases are called codons

describe the process of protein synthesis

1. transcription: occurs in the nucleus. mRNA transcribes (copies) DNA. Thymine is substituted for Uracil in mRNA (T→U)

2. mRNA leaves the nucleus and goes into the cytoplasm. Attaches itself to a ribosome

3. translation: mRNA strand is read 3 bases at a time in order to make protein. These bases are called codons

4. tRNA brings the amino acids to the ribosome to help make the protein. The 3 bases on the tRNA are called anti-codons

what is the result of mitosis?

two identical daughter cells with 23 pairs of chromosomes in each

describe the process of mitosis

1. Interphase

   • cell grows, replicates its chromosomes, preparing for the division

   • longest phase

2. Prophase: Packing

   • Chromosomes are condensing; thickening and visible

3. Metaphase: Meeting in the Middle

   • Chromosomes line up in the middle of the cell

   • nucleus disassembled

4. Anaphase: move Away

   • sister chromatids are separated and moved towards the opposite poles of the cell via spindles from the centriole

5. Telophase: Twin

   • chromosomes at opposite ends

   • nuclei formed in new cells around the chromosomes

6. Cytokinesis

   • final separation into 2 cells by splitting the cytoplasm

what is the purpose of mitosis?

to grow and heal

what is the purpose of meiosis?

to make gametes for reproduction

what is the result of meiosis

4 daughter cells in which each of the 23 chromosomes has 1 chromatid (not pairs)

how many chromosomes does meiosis result in each cell? why?

23 chromosomes (not pairs), when the male and female gametes fuse together they create a fertilised zygote with 46 chromosomes (or 23 pairs)

describe the process of meiosis

Meiosis I

1. Interphase: growing, duplicating chromosomes, prepares for division

2. Prophase I:

   • chromosomes condense

   • chromosomes pair up, aligning with its homologous partner

3. Metaphase I:

   • homologous pairs line up in the middle

     • orientation is random and therefore when they are pulled away in anaphase I, there is the possibility of many different combinations

   • chromosomes cross over, exchanging parts of their DNA

     • occurs at random points

   • after crossing over, spindles capture chromosomes and move them towards the centre

     • spindles capture the both sister chromatids

4. Anaphase I:

   • homologues pulled apart and moved to opposite ends of the cell

   • sister chromatids remains intact and attached to one another

5. Telophase I:

   • chromosomes arrive at opposite poles of the cell

   • Cytokinesis occurs at the same time, forming two daughter cells

Meiosis II

1. Prophase II:

   • cells move on from Meiosis I without copying their DNA (no Interphase II)

   • chromosomes condense

   • nuclear envelope breaks done

   • centrosomes move apart and spindles from between them

     • centrosomes duplicate between Meiosis I and Meiosis II

2. Metaphase II:

   • chromosomes line up in the middle

     • individually this time round

3. Anaphase II:

   • sister chromatids separate

   • chromatids pulled towards opposite sides of the cell

4. Telophase II:

   • nuclear membranes formed around each set of chromosomes

5. Cytokinesis:

   • splits the chromosome sets into new cell

how does meiosis create genetic variation?

crossing over at random points, random orientation of homologue pairs

why is genetic diversity important

increases chance of survival: allows for natural selection and for the organism to adapt to future environmental changes

compare mitosis and meiosis

Mitosis	Similarities	Meiosis
2 daughter cells	only 1 interphase	4 daughter cells
non-reproductive cells (somatic)	PMAT	reproductive cells (gametes)
identical daughter cells	followed by cytokinesis	genetically unique daughter cells
1 division	cell division	2 divisions
growing and healing purposes		sexual reproduction purposes
daughter cells have 46 chromosomes		daughter cells have 23 chromosomes

allele

an alternative form of a gene occupying a specific spot on a chromosome (called locus) that controls the same trait; a variant of a gene for a trait

describe the two categories of allele combinations

1. Homozygous: maternal and paternal alleles are the same

2. Heterozygous: maternal and paternal alleles are different

explain dominant and recessive alleles

• Dominant alleles mask the effect of recessive alleles

• phenotype only reflects dominant gene

• Dominant genes represented by CAPITAL letters

• Recessive genes represented by lowercase letters

describe Mendel’s pea experiment

1. cross bred YY and yy which made the offspring Yy yellow

2. cross bred Yy and Yy which made the offspring YY, Yy and yy, 75% yellow and 25% green

what were the results of Mendel’s pea experiment

• when peas were homozygous green and yellow, all of the offspring were yellow

• when peas were heterozygous yellow, the offspring were both green and yellow

• In order to produce green peas, each parent must carry a recessive trait

  • if each parent is yellow, but the offspring is green, the parents must both be heterozygous and their genotype must be Yy

continuous variation

• no distinct categories

• no limit on the value

• tends to be quantitative

• examples

  • height/weight

  • heart rate

  • finger length

  • leaf length

• controlled by

  • a lot of genes and environment

  • range of phenotypes between 2 extremes

• line graph

discontinuous variation

• distinct categories

• no in-between categories

• tends to be qualitative

• examples

  • tongue rolling

  • fingerprints

  • eye colour

  • blood group

• controlled by

  • a few genes

  • limited number of phenotype with no intermediates

• bar graph

what are the chromosome genotypes for gender?

• XY = Male

• XX = Female

karyotyping

the way geneticists identify, organise and study human chromosomes

describe the process of karyotyping

1. tissue cells placed in culture medium

2. chemically treated to stop mitosis at metaphase

   • allows chromosomes to be spread out easily for observation

3. cells stained for examination under a microscope

4. chromosomes are photographed

5. photo is enlarged and the individual chromosomes are cut out

   • normally there are 22 pairs of autosomes and one pair of sex chromosomes

6. divided according to:

   • their length

   • the position of their centromeres

   • their banding patterns

     • used to organise the chromosomes into homologous pairs. This arrangement of chromosomes is called a karyotype

name some mutagens

• electromagnetic radiation sources

• chemicals

• naturally occurring mutagens

5 criteria distinguishing mutation

1. Cause of mutation(spontaneous or induced)

2. Amount of genetic material being changed

3. Effect of mutation on DNA

4. Effect of mutation on phenotype

5. Heritability of mutations (where the mutation occurs - in somatic or germ-line cell)

If a mutation occurs in the somatic cells, when did it occur?

during mitosis

If a mutation occurs in the Somatic cells, what is its heritability?

it will NOT be inherited by the next generation

does a mutation in the somatic cells affect the species? How? Why?

it doesn’t affect the species because only body cells have been affected and occurs in a single cell

What are the effects of a mutation in a somatic cell to the mutated cell?

may cause the cell to become cancerous, die or have no effect at all

Describe mutations in the somatic cells

If mutation occurs in the Somatic (body cells), then the mutation:

• has occurred during mitosis

• is NOT inherited by the next generation

• does NOT affect the species as only body cells have been affected

• may cause the cell to become cancerous, die or have no effect at all

• mutations in a single cell

If a mutation occurs in the germ-line cells, when did it occur?

meiosis

If a mutation occurs in the sex cells, what is its heritability?

MAY be inherited by the next generation, IF that gamete is involved in fertilisation

does a mutation in the somatic cells affect the species? How? Why?

• MAY influence the species through natural selection as it provides a variation that could be:

  • harmful

    • reduces chance of survival

  • beneficial

    • increases chance of survival

  • neutral

    • no effect at present, just different

how are genetic diseases caused?

when mutations to a gene (or genes) interfere with normal cellular function, leading to the development of a disease phenotype

• can be caused by:

  • recessive alleles

  • dominant alleles

  • co-dominant alleles

cystic fibrosis

autosomal recessive disorder caused by a mutation to the CFTR gene on chromosome 7

What are the symptoms of cystic fibrosis?

produce more mucus which is unusually thick and sticky; clogs airways and secretory ducts of the digestive system leading to respiratory failure and pancreatic cysts

Sex-linked conditions are usually linked to what chromosome? Why>

the sex chromosome X: the Y chromosome is much shorter than the X chromosome and contains only a few genes. The X chromosome is much longer than the Y chromosome and contains many genes, not present on the Y chromosome

cloning

the process of producing individual organisms with identical genomes, wither by natural or artificial means

how many sheep were involved in the cloning dolly process?

3

what were the roles of each sheep in the cloning dolly process?

1. egg donor

2. nuclear donor

3. surrogate

describe the process of cloning dolly

1. unfertilised egg collected from sheep A (the egg donor).

   1. enucleation: nucleus removed from egg cell

2. somatic cell taken from sheep B (the nuclear donor)

   1. DNA acts as a blueprint used to create clone identical to sheep B

3. nucleus extracted from the somatic cell from sheep B and inserted into the donor sex cell from sheep A

4. electric impulse used to stimulate the fused cell, causing it to divide and develop into a new organism

   1. mimics natural process of cell division in fertilisation

5. embryo grows into a blastocyst which contains specialised cells that will form the future sheep

6. blastocyst is placed into the uterus of sheep C (the surrogate)

   1. sheep acts as a gestational surrogate carrying the developing clone for 148 days

7. sheep C gives birth to the cloned lamb who is genetically identical to sheep B and unrelated to the egg donor and surrogate

enucleation

nucleus removed from egg cell

What are some of the ethical implications of cloning?

• controversy of cloning humans and playing god

• changes ecosystem balanced with resources needed to keep them alive