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The following link makes such a claim

https://www.princeton.edu/~prolife/articles/embryoquotes2.html

The following references illustrate the fact that a new human embryo, the starting point for a human life, comes into existence with the formation of the one-celled zygote:

I suspect this might be cherry picking.

Interestingly there's a survey: "Biologists' Consensus on 'When Life Begins'", 2018 of US biologists on this (the choice of profession/experts was motivated by a pre-survey of the US population at large):

Many Americans disagree on ‘When does a human’s life begin?’ because the question is subject to interpretive ambiguity arising from Hume’s is-ought problem. There are two distinct interpretations of the question: descriptive (i.e., ‘When is a fetus classified as a human?’) and normative (i.e., ‘When ought a fetus be worthy of ethical and legal consideration?’). To determine if one view is more prevalent today, 2,899 American adults were surveyed and asked to select the group most qualified to answer the question of when a human’s life begins. The majority selected biologists (81%), which suggested Americans primarily hold a descriptive view. Indeed, the majority justified their selection by describing biologists as objective scientists that can use their biological expertise to determine when a human's life begins.

A sample of 5,502 biologists from 1,058 academic institutions assessed statements representing the biological view ‘a human’s life begins at fertilization’. This view was used because previous polls and surveys suggest many Americans and medical experts hold this view. Each of the three statements representing that view was affirmed by a consensus of biologists (75-91%). The participants were separated into 60 groups and each statement was affirmed by a consensus of each group, including biologists that identified as very pro-choice (69-90%), very pro-life (92-97%), very liberal (70-91%), very conservative (94-96%), strong Democrats (74-91%), and strong Republicans (89-94%). Overall, 95% of all biologists affirmed the biological view that a human's life begins at fertilization (5212 out of 5502).

Historically, the descriptive view on when life begins has dictated the normative view that drives America's abortion laws: (1) abortion was illegal at ‘quickening’ under 18th century common law, (2) abortion was illegal at ‘conception’ in state laws from the late 1800’s to the mid-1900’s, and (3) abortion is currently legal before ‘viability’ due to 20th century U.S. Supreme Court cases Roe v. Wade and Planned Parenthood v. Casey. While this article’s findings suggest a fetus is biologically classified as a human at fertilization, this descriptive view does not entail the normative view that fetuses deserve legal consideration throughout pregnancy.

But do note (as the 3rd para [I added the breaks for readability] says) that that doesn't imply anything about viability/personhood. The fact that these are distinct questions is emphasized in other (scientific) sources:

In this paper we show that the question, "When does human life begin?", is not one question, but three. The first question is, "When does human biological life begin?", and is a scientific question. A brief review of embryology is provided to answer this question. The second question is, "When do obligations to protect human life begin?", and is a question of general theological and philosophical ethics. A brief review of major world religions and philosophy is provided to answer this question but has no settled answer and therefore involves irresolvable controversy. The third question is, "How should physicians respond to disagreement about when obligations to protect human life begin?" and is a question for professional medical ethics.

The science in this latter paper is nothing unconventional, i.e. it's consistent with the majority view from the other one.

Some (interesting, I hope) details from the survey (first paper). They asked 4 question of biologists:

Q1 - Implicit Statement A: “The end product of mammalian fertilization is a fertilized egg (‘zygote’), a new
mammalian organism in the first stage of its species’ life cycle with its species’
genome.”

Q2 - Implicit Statement B: “The development of a mammal begins with fertilization, a process by which the
spermatozoon from the male and the oocyte from the female unite to give rise to a
new organism, the zygote.”

Q3 - Explicit Statement “In developmental biology, fertilization marks the beginning of a human's life since
that process produces an organism with a human genome that has begun to develop
in the first stage of the human life cycle.”

Q4 - Open-Ended Essay Question: “From a biological perspective, how would you answer the question ‘When does a
human's life begin?’”

And some charts for the responses (for the first two questions there was no [graphical] breakdown of political orientation; there is some in a table, but it's two pages long):

For the last question, there was manual coding of the free-form responses into those categories.

The "95% consensus" may be a little exaggerated because it was derived by evaluating whether each subject affirmed at least one of Q1-Q3 (i.e. logical ORing).

LangLangC asks some intersting (terminolgoy) questions. One way to solve these is as in the 2nd paper I mentioned.

A human being originates from two living cells: the
oocyte and the spermatozoon, transmitting the torch of
life to the next generation. [...] After syngamy, the zygote undergoes mitotic cell division
as it moves down the fallopian tube toward the
uterus. A series of mitotic divisions then leads to the
development of the preembryo. [...]

The pre-embryo is the structure that exists from the
end of the process of fertilization until the appearance of
a single primitive streak. Until the completion of implantation
the pre-embryo is capable of dividing into multiple
entities, but does not contain enough genetic information
to develop into an embryo: it lacks genetic material from
maternal mitochondria and of maternal and parental
genetic messages in the form of messenger RNA or
proteins.

A key stage in embryonic development is the emergence
of an individual human being. ‘‘Individual’’ means
that an entity (1) can be distinguished from other entities
and (2) is indivisible, i.e., it cannot be divided or split into
two members of the same species. An entity meeting the
first criterion, but not the second, is a distinct but not
individual entity. The pre-embryo, because it can divide
into monozygotic twins is a distinct but not individual
entity. The embryo, by contrast, no longer divides into
monozygotic twins and so it meets both criteria for being
an individual.

Distinct human life begins when there is a distinct entity,
the pre-embryo, resulting from the process of conception.
There is no ‘‘moment’’ of conception, a phrase that
has no biological application. Individual human life
begins later, with the emergence of the embryo. There is
no ‘‘moment’’ at which this occurs either. The beginnings
of human life involve complex biological processes that
occur over time.

The latter terminology "distinct human life", "individual human life" is probably not so well-established... But in this sense, an (unfertilized) egg or sperm is not "distinct human life" from its host/producer.