VCE Biology Question Thread

[alchemy]

Can somebody please explain to me this statement about X-linked recessive patterns

•   Daughters of males with the trait are carriers of the trait, and do not show the trait

If a male with the trait crossed with a female who was either homozygous recessive or heterozygous for the trait, wouldn't it be possible for the daughter of that male to show the trait?

thanks

Sorry, I misunderstood your question the first time.
So, let's consider the two situations
Case 1: Affected male (X^aY). Homozygous recessive unaffected female (X^AX^A. Thus, female offspring can only be X^AX^a). As you can see the daughters are now carriers of the trait.
Case 2: Affected male (X^aY). Heterozygous unaffected female who is a carrier (X^AX^a. Thus, female offspring can be X^AX^a or X^aX^a).
This is exactly what the book says! However, in your question you said "If a male with the trait crossed with a female who was either homozygous recessive or heterozygous for the trait, wouldn't it be possible for the daughter of that male to show the trait?" ...which is misleading to us because daughter of the male can only show the trait if the mother was heterozygous in the case of X-linked recessive inheritance.

[RazzMeTazz]

How would you work backwards and find the genotype of the parents with knowledge of the genotype of the offspring?

[RazzMeTazz]

If the offspring produced in a cross all have the same genotype what would you write the genotype and phenotype ratio as?
Would you write 1:0 or just 1?

[Sense]

During meiosis, homologous chromosomes pair as shown in the following diagram

*Just a picture of two chromosomes next to each other*

The number of DNA molecules this pair of chromosomes contains is:

A. Hundreds
B. 46
C. 4
D. 2

Is it c or d ?



Meiosis in human females:

A. Involves the separation of homologous chromosomes before DNA replication
B. relies on contraction of protein fibres in the spindles formed within the cells
C. Results in four gametes for each cell that undergoes the process
D. Involves haploid cells giving rise to diploid cells

[grannysmith]

During meiosis, homologous chromosomes pair as shown in the following diagram

*Just a picture of two chromosomes next to each other*

The number of DNA molecules this pair of chromosomes contains is:

A. Hundreds
B. 46
C. 4
D. 2

Is it c or d ?



Meiosis in human females:

A. Involves the separation of homologous chromosomes before DNA replication
B. relies on contraction of protein fibres in the spindles formed within the cells
C. Results in four gametes for each cell that undergoes the process
D. Involves haploid cells giving rise to diploid cells

1. I'd say C. When homologous chromosomes pair up during metaphase I, each chromosome is composed of two chromatids, with each chromatid containing a single  DNA molecule.

2. B. Homologous chromosomes separate during anaphase I; females only produce a single ovum (gametes) with the other three being polar bodies; meiosis isa reductive division (diploid to haploid).

[Sense]

1. I'd say C. When homologous chromosomes pair up during metaphase I, each chromosome is composed of two chromatids, with each chromatid containing a single  DNA molecule.

2. B. Homologous chromosomes separate during anaphase I; females only produce a single ovum (gametes) with the other three being polar bodies; meiosis isa reductive division (diploid to haploid).

Thanks! I thought that when the chromatids were together they might technically only be one DNA molecule each..

[RazzMeTazz]

For dominant lethal alleles, does the individual die even if they have only one copy of this dominant lethal allele (heterozygous) ? or only if they are homozygous dominant?

[RazzMeTazz]

Do we need to know about reciprocal crosses?

[howlingwisdom]

For dominant lethal alleles, does the individual die even if they have only one copy of this dominant lethal allele (heterozygous) ? or only if they are homozygous dominant?

I'm pretty sure the individual will die if it is typically homozygous dominant for the lethal gene (eg AA).

Do we need to know about reciprocal crosses?

I'm fairly sure that we do

[Sense]

A chemical company is testing a new product that it believes will increase the growth rate of food plants, suppose you are able to view the plants root tips that have been treated with the product. If the product is successful, what difference in patterns would you see in the cells compared to a plant that hasn't been treated?

Would it be the treated plant would have less cells in the interphase?

[Reus]

A chemical company is testing a new product that it believes will increase the growth rate of food plants, suppose you are able to view the plants root tips that have been treated with the product. If the product is successful, what difference in patterns would you see in the cells compared to a plant that hasn't been treated?

Would it be the treated plant would have less cells in the interphase?

I think you're right, the new product increases the growth rate of food plants and as interphase takes the longest period of time, this means that there would be less of it seen as they would be already in/starting the mitotic phase. Patterns may also include more cells undergoing mitosis.

[grannysmith]

How much do we need to know about mutations and continuous/discontinuous variation?

[chekside]

At G2 stage of interphase is the number of chromosomes diploid?

[grannysmith]

At G2 stage of interphase is the number of chromosomes diploid?

Yes. 46 chromosomes but 92 chromatids.

[Reus]

Explain why Huntington disease persists in the human population when it is caused by a lethal, dominant allele.
Thanks.