⭐️SB3 - Genetics Flashcards
What’s asexual reproduction?
Where some organisms can reproduce without fertilisation producing clones
In animals, which types reproduce in what ways?
Invertebrates - asexually
Vertebrates - mainly sexually
Give the definition of sexual reproduction
Combines characteristics of both parents so the offspring are different to each other
Give two advantages of sexual reproduction
- offspring can adapt if they move to new environmental conditions
- causes variation among offspring so the species is more likely to survive a disease or new pest e.c.t
What are the advantages of asexual reproduction?
- Much faster than sexual reproduction as there’s no need to find a mate
- requires less energy to reproduce
State the main difference between the offspring produced in sexual reproduction vs asexual reproduction
Sexual reproduction produces offspring with variation but asexually reproduced offspring are clones to the parent
Where doesn’t meiosis take place?
In asexual reproduction
What are gametes?
Sex cells
What’s a zygote?
A single fertilised egg cell
What process causes a zygote to form a ball of cells?
Mitosis
What us DNA?
The code in a molecule that are the instructions for an organism
Where is a molecule of DNA found?
In the Chromosome of a cell
What is the genome?
The DNA of an organism, most cells contain a complete copy of a genome
What are genes?
Sections of DNA molecules that contain a code for making proteins
What controls the order of amino acids in polymers?
Genes, humans have around 20,000
How many chromosomes does a diploid and a haploid cell have?
Diploid cell has 46, haploid cell has 23
What kind of cells are gametes?
Haploid cell’s
Why do brothers and sisters look similar but aren’t identical
As each human chromosome in a pair contains different versions of the same gene making them genetically different
How are proteins polymers?
They are made by linking different amino acids together in a chain
What process is used to produce gametes?
Meiosis
What step happens before meiosis?
Interphase
What kind of cell starts off in meiosis?
A diploid gamete making cell
What are the steps of meiosis?
- the chromosomes of the diploid cell replicate
- The cell divides into two diploid cells
- These new cells each divide again
- The four daughter cells are haploid as they have a copy of one chromosome from each pair
What are chromosomes made of?
Molecules of dna tightly coiled and packaged up with proteins
What is the shape of a DNA molecule?
Two strands forming a double helix structure?
What joins the two strands in DNA?
Pairs of bases
What are the base pairs?
Adenine - thymine
Cytosine - guanine
What are matching bases?
Complimentary base pairs
What’s a nucleotide?
The base attached to a sugar attached to a phosphate group in a dna molecule
What holds bases together?
Hydrogen bonds
Draw a labelled diagram of a dna molecule including the nucleotide
Check the notepad to see if it’s correct
How do the base pairs have a hydrogen bond between them?
As the slightly negative charged part on one of the base pairs attracts another positively charged part of a base pair forming a weak force of attraction being a hydrogen Bond
Describe the backbone of a dna strand
The sugar and phosphate group
Why do bass pairs pair specifically?
Because C-G form 3 hydrogen bonds between them but A-T form 2 hydrogen bonds between them
What’s important about the order of bases in a gene?
As they contain the coded instructions for the protein
What’s starch a polymer of?
Glucose
What’s cellulose a polymer of?
Glucose
What’s the type of sugar in a nucleotide?
Deoxyribose sugar
Each gene codes for a specific sequence of…
Amino acids to make a specific protein
What are the steps in transcription?
- RNA polymerase attaches to the non coding part of the DNA
- This causes the enzyme to separate into two strands
- The RNA polymerase moves along the DNA strand adding complimentary RNA nucleotides
- The nucleotides link to form a strand of RNA
What’s the first and second stage of protein synthesis?
Transcription .1
Translation .2
What’s the difference between DNA and RNA
In RNA instead of thymine, uracil is used
What’s RNA polymerase?
An enzyme responsible for creating mRNA in transcription
What is a non-coding strand of DNA?
A region of DNA that doesn’t contain a code for a protein
Where does translation occur?
In the cytoplasm
Where does transcription occur?
In the nucleus
What are the steps in translation?
- mRNA leaves the nucleus through nuclear pores into the cytoplasm
- The mRNA strand attaches to a ribosome in the cytoplasm
- The ribosome moves along the mRNA strand a codon at a time where a molecule of tRNA lines up
- Each tRNA carries a specific amino acid and they join as the ribosome moves along forming a polypeptide
What’s a polypeptide?
A chain of amino acids
What happens at the end of protein synthesis when the polypeptide forms?
It folds to form a protein with a specific shape
What are ribosomes made of?
RNA and protein
What’s a mutation?
A change in the genetic bases of a gene. The same as a genetic variant
When can mutations happen?
When DNA isn’t copied correctly or by environmental factors
What can mutations cause to an organism?
A change in their phenotype (the way they look)
What are alleles and what causes them?
They are different forms of the same gene and are caused by mutations
How many polypeptides does haemoglobin contain?
Four of the kinds alpha and beta
What do the haemoglobin polypeptides form?
Globular proteins which carry oxygen
What causes sickle cell disease?
A base change causing a different amino acid so the haemoglobin polypeptide folds incorrectly
why do mutations not happen all the time in a base change?
As codons can sometimes encode for the same amino acid in which case the folding of the protein is un affected
What is meant by the term genetic disorder?
A disorder caused by faulty alleles
Only when can mutations effect protein synthesis?
If they take place in the non coding section of DNA
What kind of mutation causes B-thalassemia?
A mutation in the non coding region of dna so rna polymerase doesn’t bind well and so transcription is reduced
When may too much mRNA be produced?
When there is a mutation in the non coding section of dna that causes RNA polymerase to bind better
What does variation mean?
Differences in the characteristics in a group of the same organism
What did scientists used to believe about the characteristics among offspring
That they were blended instead of inherited
What conclusion did mendel’s experiments lead him to make?
Characteristics are not blended during inheritence but instead we’re determined by inherited units that don’t change when passed on to descendants
How did Mendel’s work lead to the discovery of recessive alleles?
As he noticed some characteristics were masked and then reappeared in later generations
How did scientists begin to notice mendels work?
When they noticed his units behaved similarly to chromosomes in cell division and the units were then renamed genes
Why did Mendel use pea plants?
They have multiple variable traits that are clearly visible like seed colour, pod colour and shape
Why may each copy of a gene be a different allele?
Because as there two copies of every chromosome in a body cell nucleus and so each body cell contains two copies of the same gene
What gives us genetic variation?
The different combination of alleles
What does it mean if an organism is homozygous?
Both alleles for one gene are the same
What does it mean if an organism is heterozygous?
The alleles are different to each other
When is a recessive characteristic seen?
If both alleles are recessive
How do you represent dominant and recessive alleles?
Dominant are capitals, recessive are lowercase. Dominant is always written before the recessive one
What is a genotype?
The alleles in an organism
What’s a phenotype?
What an organism looks like
What is monohybrid inheritance?
The inheritance of one gene e.g. TT or tt
What determines your sex? What are they?
Sex chromosomes. females have two X chromosomes and males have two Y chromosomes
What is cystic fibrosis? What problems does it cause?
It’s a genetic disorder caused by the recessive allele where people have issues with their lungs and digestive system
Give the likely hold of offspring having cystic fibrosis of the parents are heterozygous for the CF gene
25% likely
What allele causes polydactyly?
The dominant allele
What are the four blood groups?
A, B, AB and O
What determines your ‘marker molecules’? What are they?
Your blood group, these are A, B and O
Describe the genes responsible for the markers in the ABO system. What’s recessive to what?
They are alleles written as I^A I^B and I^O. Everyone has two copies of the same gene and I^O is recessive to both I^A and I^B.
What does co-dominant alleles mean? Give an example.
Where both alleles for a gene affect the phenotype. For example a person with the genotype I^A I^B shows the effect of both alleles and has the blood group AB
A person has the blood group AB. What’s their genotype?
I^A I^B
What is the meaning of sex-linked genetic disorder?
Disorders that show a different pattern of inheritance in men and women are called sex linked genetic disorders
What are the 6 possible genotypes for blood?
I^A I^B, I^O I^O, I^A I^A, I^B I^B,
I^B I^O, I^A I^O
Why will a man only have one allele for some genes on the X chromosome?
Because a human Y sex chromosome is missing some of the genes found on the X sex chromosome.
Why are men more likely to develop sex linked genetic disorders?
As if the allele for an X chromosome gene causes a genetic disorder then a man will develop it because there is no allele on the Y chromosome to potentially cancel it out
State 2 diseases caused by a sex linked genetic disorder
Red green colour blindness and haemophilia
Why can red green colour blindness happen?
Due to cone cells in the retina not working properly
What is a mutation?
A change that creates a new allele.
When do mutations happen? Why?
When there is a mistake in copying DNA during cell division. This can be because of the DNA being damaged due to radiation or certain substance
Explain why a mutation doesn’t always produce a change in a characteristic
Because mutations can occur in different parts of a gene and so don’t always largely effect the protein produced or don’t change the protein at all
Give two benefits of mapping someone’s genome
- to indicate their risk of developing diseases caused by different alleles
- to identify which medicines are best to treat someone’s illness as alleles can affect how medicine works in the body
What has the human genome project shown?
Their are variations between people but over 99% of DNA bases in different people are the same
Why should you keep in mind the alleles of a patient in clopidogrel?
As some have alleles that mean the drug doesn’t protect them against blood clots if they’re at risk of a heat attack or stroke
What causes genetic variation?
Different alleles inherited during sexual reproduction
What is environmental variation?
Characteristics affected by the surroundings
What are acquired characteristics?
A characteristic of an organism that can change during its life due to a change in the environment e.g. loss of a limb
What are the two types of variation and their meanings?
Discontinuous variation=data can only take a limited set of values
Continuous variation=data can be any value in a range
How do you know if a frequency bar chart is showing continuous or discontinuous variation?
As continuous variation doesn’t have any gaps between the bars but discontinuous variation does have gaps between the bars
What does continuous data form on a graph usually?
A bell shaped curve
What is a normal distribution?
The bell shaped curbs formed by continuous data
What were the three laws of inheritance that Mendel came up with?
- Each gamete only receives one hereditary unit for a characteristic
- hereditary factors are passed on unchanged from parent to offspring and there’s one factor per parent
- same versions of a factor are more powerful than others and always have an affect on the expression of a characteristic
