genetics

Question 1

polygenic

Answer 1

coded for by more than one gene

Question 2

single gene

Answer 2

coded for by one gene

Question 3

homozygous dominant (capital letters)

Answer 3

zygote has same two factors or alleles and these factors/alleles are dominant

Question 4

homozygous recessive (small letters)

Answer 4

zygotes’s same two factors or alleles are recessive. a recessive allele is only visible when paired with another recessive allele.

Question 5

heterozygous

Answer 5

different alleles (one dominant and one recessive)

Question 6

law of segregation vs law of independent assortment

Answer 6

the law of segregation refers to alleles of the same gene, whereas the law of independent assortment refers to different genes in different combinations

Question 7

a summary of the significance of Mendel’s work (9)

Answer 7

we use Mendel’s work as a model of how genes behave. he showed the following fundamental facts:

• traits from parents pass on as unmodified ‘units’
• genes pass to successive generations according to set ratios
• individuals have two sets of genes for each trait: one set is received from each parent
• it makes no difference if a characteristic is inherited from male or female: they contribute in the same way
• these genes are sometimes expressed and sometimes concealed, but never lost
• each gene is passed on independently from all other genes
• the expression of these characteristics within generations of plants is variable
• certain traits show up much more often than others (even when they have been present in equal numbers in previous generations)
• certain characteristics are not immediately expressed (recessive) in preference to others (dominant)

Question 8

inheritance and variation: monohybrid crosses (4)

Answer 8

a monohybrid cross is a:
- genetic cross between two individuals
- each of which has different alleles for a single trait
- and two different possible alleles
this cross can be done between two individuals that are homozygous or heterozygous.

Question 9

incomplete or partial dominance

Answer 9

if alleles show incomplete dominance or partial dominance, neither of the characteristics is dominant over the other, resulting in the offspring showing a ‘new’ mixed characteristic

Question 10

co-dominant inheritance

Answer 10

co-dominant alleles are equally dominant. they are both present in the phenotype when they are combined. co-dominant inheritance is not the same as incomplete dominance

Question 11

ABO blood groups (3)

Answer 11

• blood groups exist due to the proteins expressed on the surface of red blood cells
• these proteins are called antigens because they cause an immune response
• there are four different blood groups: A, B, AB and O

Question 12

genetics of ABO blood groups (7)

Answer 12

• human blood types are determined by multiple alleles
• there are three alternative versions of a gene for the same locus on the same chromosome pair
• any two can be paired in a diploid cell
• the three different alleles are known as I^A, I^B and i
• the I^A and I^B alleles are co-dominant with each other and they code for cell surface antigens A and B
• the i allele is recessive and codes for the lack of the cell surface antigen
• type A and B individuals can be either homozygous (I^AI^A or I^BI^B) or heterozygous (I^Ai or I^Bi)

Question 13

dihybrid crosses (7)

Answer 13

• a dihybrid cross involves inheritance for organisms that differ in two traits
• a dihybrid cross produces new individuals that are phenotypically unlike either of the original, true-breeding parents
• after inbreeding of the F1 and the F2 generation, there are a possible nine different genotypes and a phenotype ratio of 9:3:3:1
• new genotypes are possible because the genes are carried on separate pairs of homologous chromosomes
• these separate pairs of homologous chromosomes sort out independently during meiosis
• independent assortment of characteristics results from the random positioning of homologous chromosomes during metaphase 1 of meiosis.
• random distribution of alleles during gamete formation thus occurs

Question 14

autosomes

Answer 14

chromosome pairs 1 to 22 that contain the genes for the same features in males and females

Question 15

gonosomes

Answer 15

chromosome pair 23 that contains the sex chromosomes that determine the sex of the individual

Question 16

determination for sex in humans

Answer 16

the sex of a zygote is determined at fertilisation by the type of sex chromosomes (X or Y) present in the sperm

• if the sperm contains an X chromosome, the zygote will be female (XX)
• if the sperm contains a Y chromosome, the zygote will be male (XY)

Question 17

sex-linked genes (3)

Answer 17

• x-linked recessive traits are expressed in the male phenotype because males have one X chromosome, so there is no corresponding dominant allele.
• in females, a recessive allele on one x chromosome is often cancelled out in their phenotype by a dominant allele on the other x chromosome.
• often females are carriers of x-linked traits but if they are homozygous for the trait it will be expressed in their phenotypes

Question 18

define a mutation (2)

Answer 18

a mutation is any alteration in the inherited nucleic acid sequence (gene) of the genotype of an organism. these changes occur during dna replication.

Question 19

occurence of mutations

Answer 19

• mutations can occur on a macroscopic level as chromosomal abberations or may be the result of a single base pair change in the dna sequence
• mutations can occur within a gene, preventing the synthesis of the correct protein
• they may occur outside of the gene coding areas, such as in regulatory regions of dna

Question 20

inherited mutations

Answer 20

a hereditary mutation is present in every cell of the body. these mutations are copied every time a body cell divides.

Question 21

acquired mutation

Answer 21

acquired mutations are changes in the genomic sequence of individual cells and they are only passed to cells that come directly from the original cell.

Question 22

selective breeding

Answer 22

the process of breeding plants or animals for particular traits

Question 23

genetic engineering

Answer 23

directly manipulating the genes of a plant or animal using technology

Question 24

biotechnology

Answer 24

using organisms or their components to make products

Question 25

genetic modification

Answer 25

technology that changes the genetic makeup of organisms

Question 26

recombinant dna technology

Answer 26

combining genes from different organisms

Question 27

cells and tissues in genetic engineering and biotechnology

Answer 27

undifferentiated cells and tissues are used in biotechnology and genetic engineering because their genomes are not fixed in a specific developmental pathway

Question 28

making insulin to treat diabetics using plasmids (5)

Answer 28

• the insulin gene is transferred into a plasmid vector
• plasmids are small circular dna in bacteria cells
• they are separate from the bacterial chromosome and smaller than it
• they can pass from one cell to another, even between different species
• plasmids are used as vectors for reproducing foreign dna using the bacterial replicating process

Question 29

cloning

Answer 29

• cloning is growing cells from a single cell by stimulating mitosis
• primary embryonic cells ( meristematic cells and parenchyma cells in plants and stem cells in animals) and a growth medium are used
• the medium contains all growth substances to support growth and development of the tissue

Question 30

stem cells

Answer 30

undifferentiated cells that have the potential to develop into many different cell types
stem cells are important because they can be used to generate almost any type of specialised cell in the human body

Question 31

stem cell culture

Answer 31

• scientists extract embryonic stem cells from the blastocyst phase of development, destroying the blastocyst in the process
• they place the cells in acontrolled environment that stops them from differentiating, but lets them divide and replicate